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Geophysical Methods

Geophysics is a branch of Earth science that utilizes principles and techniques from physics to study the physical properties and processes of the Earth. It involves the application of various methods to investigate the subsurface structure, composition, and dynamics. Geophysical methods are essential tools for understanding the Earth’s interior and for exploring natural resources.

Definition of Geophysics:

Geophysics is the scientific discipline that uses principles and methods of physics to study the Earth’s structure, composition, and processes. It involves measuring and interpreting physical fields such as gravity, magnetism, seismic waves, and electromagnetic radiation to gain insights into the subsurface and interior of the Earth.

Purpose and Applications:

  1. Subsurface Exploration: Geophysics is widely used for subsurface exploration in industries such as oil and gas, mining, and environmental studies. By analyzing the response of the Earth to different physical fields, geophysicists can infer the characteristics of the subsurface, helping in the discovery of resources like oil, gas, minerals, and groundwater.
  2. Natural Hazard Assessment: Geophysical methods play a crucial role in assessing and monitoring natural hazards such as earthquakes, volcanic eruptions, and landslides. By studying the Earth’s crust and mantle, geophysicists can identify potential risks and contribute to the development of early warning systems.
  3. Environmental Studies: Geophysics is used in environmental studies to investigate soil and water contamination, map underground aquifers, and monitor changes in the Earth’s surface. This information is valuable for environmental impact assessments and resource management.
  4. Archaeological Investigations: Geophysical methods are employed in archaeology to map and analyze buried structures without excavation. Ground-penetrating radar, resistivity surveys, and magnetic methods help archaeologists locate ancient sites and understand their layout.
  5. Planetary Exploration: Geophysical methods are not limited to Earth. Similar techniques are applied in planetary exploration to study the subsurface of other planets and celestial bodies. For example, seismometers on Mars have been used to detect marsquakes and understand the interior structure of the planet.

Importance in Earth Sciences and Exploration:

  1. Understanding Earth’s Interior: Geophysics provides crucial information about the Earth’s interior, helping scientists understand the structure and composition of the crust, mantle, and core. This knowledge contributes to our understanding of Earth’s geological evolution.
  2. Resource Exploration: In industries such as oil and gas exploration, mining, and geothermal energy, geophysics is indispensable for locating and characterizing subsurface resources. It reduces the need for expensive and invasive drilling by providing valuable insights beforehand.
  3. Risk Assessment and Mitigation: Geophysical methods contribute to assessing and mitigating natural hazards by providing data on fault lines, seismic activity, and volcanic structures. This information is vital for disaster preparedness and risk reduction.
  4. Environmental Monitoring: Geophysics helps monitor environmental changes, including groundwater movement, soil composition, and subsurface contamination. This is essential for sustainable resource management and environmental protection.

In summary, geophysics is a versatile and indispensable field that plays a crucial role in advancing our understanding of the Earth and its resources, contributing to various scientific, industrial, and environmental applications.

Types of Geophysical Methods

Geophysical methods can be broadly categorized into two main groups: non-seismic methods and seismic methods. These methods utilize different physical principles to investigate the subsurface and provide valuable information about the Earth’s interior. Here’s an overview of each category:

Non-Seismic Methods

a. Gravity Survey:

  • Principle: Gravity surveys measure variations in the Earth’s gravitational field caused by variations in subsurface density.Applications: Used in mineral exploration, subsurface mapping, and detecting geological structures.
b. Magnetic Survey:
  • Principle: Magnetic surveys measure variations in the Earth’s magnetic field caused by magnetic properties of subsurface materials.Applications: Useful in mineral exploration, mapping geological structures, and locating buried objects.
c. Electrical Resistivity Survey:
  • Principle: Measures the ability of the subsurface to conduct electrical current, providing information about the composition and moisture content.Applications: Used in groundwater studies, environmental investigations, and archaeological surveys.
d. Ground-Penetrating Radar (GPR):
  • Principle: GPR uses radar pulses to image the subsurface, detecting reflections from interfaces between different materials.Applications: Commonly used in archaeology, environmental studies, and civil engineering for subsurface imaging.
e. Electromagnetic (EM) Methods:
  • Principle: EM methods measure the response of the subsurface to induced electromagnetic fields.Applications: Applied in mineral exploration, groundwater studies, and mapping conductive structures.
f. Remote Sensing:

  • Principle: Involves collecting information about the Earth’s surface from a distance using satellite or aerial platforms.
  • Applications: Used in geological mapping, land cover classification, and environmental monitoring.

Seismic Methods

a. Seismic Reflection:

  • Principle: Involves sending seismic waves into the subsurface and analyzing the reflected waves to image subsurface structures.Applications: Widely used in oil and gas exploration, subsurface mapping, and engineering studies.
b. Seismic Refraction:
  • Principle: Analyzes the travel times of seismic waves refracted at subsurface interfaces to determine subsurface velocities and depth.Applications: Used in engineering, groundwater studies, and shallow subsurface investigations.
c. Surface-Wave Methods:
  • Principle: Measures the propagation characteristics of surface waves traveling along the Earth’s surface.Applications: Used for shallow subsurface imaging, site characterization, and geotechnical studies.
d. Downhole Seismic Methods:
  • Principle: Involves deploying seismic sensors in boreholes to acquire high-resolution subsurface information.Applications: Used in oil and gas reservoir characterization, geological studies, and monitoring subsurface changes.
e. Crosshole Seismic Methods:

  • Principle: Involves deploying seismic sources and receivers in different boreholes to study subsurface properties between boreholes.
  • Applications: Commonly used in geotechnical investigations and characterization of subsurface materials.

These geophysical methods are often used in combination to obtain a comprehensive understanding of the subsurface conditions and geological structures in a given area. The choice of method depends on the specific objectives of the study and the characteristics of the subsurface materials being investigated.

Instrumentation and Equipment

The instrumentation and equipment used in geophysics vary depending on the specific geophysical method being employed. Each method requires specialized tools to measure and record the physical properties of the subsurface. Here is an overview of some common geophysical instruments and equipment:

1. Gravity Survey:

  • Gravimeter: Measures variations in gravitational acceleration. Modern gravimeters are often based on superconducting technology for high precision.

2. Magnetic Survey:

  • Magnetometer: Measures the strength and direction of the Earth’s magnetic field. Fluxgate and proton precession magnetometers are commonly used.

3. Electrical Resistivity Survey:

  • Resistivity Meter: Measures the electrical resistivity of the subsurface materials. Various electrode configurations and arrays are used depending on the survey objectives.

4. Ground-Penetrating Radar (GPR):

  • GPR System: Includes a control unit and antennas that emit and receive radar pulses. Antennas may vary in frequency for different penetration depths.

5. Electromagnetic (EM) Methods:

  • EM Receiver and Transmitter: EM instruments consist of a transmitter that induces an electromagnetic field and a receiver that measures the response. Different coil configurations are used for various applications.

6. Seismic Reflection:

  • Seismic Source (Vibroseis, Explosive, etc.): Generates seismic waves that penetrate the subsurface.
  • Geophones: Detect ground motion and record seismic reflections. Arrays of geophones are used for data acquisition.

7. Seismic Refraction:

  • Seismic Source (Explosive, Hammer, etc.): Produces seismic waves that refract at subsurface interfaces.
  • Geophones: Measure the arrival times and amplitudes of refracted seismic waves.

8. Surface-Wave Methods:

  • Accelerometers or Geophones: Measure ground motion caused by surface waves.

9. Downhole Seismic Methods:

  • Downhole Seismic Sensors: Deployed in boreholes to record seismic waves at various depths.

10. Crosshole Seismic Methods:

  • Seismic Sources and Receivers: Deployed in different boreholes for subsurface imaging between boreholes.

11. Remote Sensing:

  • Satellite or Aircraft-Based Sensors: Include optical, infrared, radar, and other sensors for collecting data about the Earth’s surface.

12. Global Positioning System (GPS):

  • GPS Receivers: Provide precise location information for ground-based instruments.

13. Data Acquisition and Processing Systems:

  • Data Loggers and Recorders: Capture and store geophysical data during field surveys.
  • Computers and Software: Process and interpret geophysical data to generate subsurface models.

14. Inclinometers and Tiltmeters:

  • Inclinometers: Measure the angle of inclination of a borehole, providing information about subsurface stability.
  • Tiltmeters: Measure small changes in tilt, often used for monitoring ground deformation.

15. Borehole Logging Tools:

  • Various Tools: Gamma ray, resistivity, sonic, and other sensors are attached to a downhole toolstring for logging data within boreholes.

These instruments and equipment are integral to conducting geophysical surveys and experiments, allowing scientists and engineers to gather data about the Earth’s subsurface and make informed interpretations about geological structures, resource distribution, and environmental conditions. The advancement of technology has led to the development of more sophisticated and precise instrumentation in the field of geophysics.

Data Processing and Interpretation

Data processing and interpretation are crucial steps in geophysics, as they transform raw field measurements into meaningful information about the subsurface. The process involves handling, filtering, analyzing, and modeling geophysical data to extract valuable insights. Here’s an overview of the typical steps involved in data processing and interpretation in geophysics:

1. Data Pre-processing:

  • Data Quality Check: Assess the quality of acquired data, identify and correct errors or anomalies.
  • Noise Reduction: Apply filters and corrections to minimize noise and interference in the data.
  • Coordinate System Transformation: Convert raw data into a consistent coordinate system for analysis.

2. Data Inversion:

  • Mathematical Inversion: Use mathematical algorithms to invert observed data and estimate subsurface properties.
  • Modeling: Employ numerical models to simulate subsurface conditions and compare with observed data.

3. Velocity Analysis (for Seismic Methods):

  • Velocity Analysis: Determine the velocity of seismic waves in the subsurface to improve depth imaging.
  • Migration: Apply migration algorithms to correct for the effects of velocity variations and improve subsurface imaging.

4. Filtering and Smoothing:

  • Frequency Filtering: Remove unwanted frequencies or enhance specific frequency ranges in the data.
  • Spatial Smoothing: Reduce noise and highlight coherent patterns by applying spatial smoothing techniques.

5. Time-Distance Conversion (for Seismic Methods):

  • Time-Distance Conversion: Convert travel times of seismic waves to depth information for subsurface structure interpretation.

6. Data Integration:

  • Integration of Multiple Data Sets: Combine data from various geophysical methods or other sources for a comprehensive subsurface characterization.
  • Joint Inversion: Simultaneously invert multiple datasets to obtain a more accurate and consistent subsurface model.

7. Attribute Analysis:

  • Attribute Extraction: Derive additional information (attributes) from the geophysical data, such as amplitude, phase, or frequency.
  • Attribute Mapping: Create maps or sections highlighting specific attributes for interpretation.

8. Interpretation:

  • Identification of Anomalies: Recognize anomalies or patterns in the data that may indicate geological features or subsurface changes.
  • Correlation with Geological Models: Compare geophysical results with existing geological models to validate interpretations.

9. 3D Visualization:

  • 3D Modeling: Develop three-dimensional models of the subsurface based on the interpreted data.
  • Visualization Tools: Use software tools to visualize and manipulate 3D models for better understanding.

10. Uncertainty Analysis:

  • Uncertainty Quantification: Assess the uncertainty associated with the interpreted results.
  • Sensitivity Analysis: Evaluate the sensitivity of interpretations to changes in input parameters or assumptions.

11. Report Generation:

  • Documentation: Prepare comprehensive reports documenting the data processing steps, methodologies, and interpretations.
  • Presentation: Communicate findings through visual aids, graphs, and maps.

12. Iterative Approach:

  • Iterative Refinement: The interpretation process may involve iterative refinement, where adjustments are made based on feedback and additional data.

Data processing and interpretation in geophysics require a combination of expertise in geology, physics, and mathematics. It’s a dynamic process that involves both scientific judgment and the use of advanced software tools. The goal is to derive accurate and meaningful information about the subsurface for applications in resource exploration, environmental studies, and geological investigations.

Geophysics

The rocks does not differ only by their macroscopic or microscopic properties studied field geologists or petrologists. They also differ by their chemical and physical properties. Hence as the rocks differ according to their origin, structure, texture, etc. they also differ by their density, magnetisation, resistivity, etc. The bad news is that the physical properties do not always clearly correlates with geological classifications and do not necessarily easily translates into the geological terms.

The use of physics to study the interior of the Earth, from land surface to the inner core is known as solid earth Geophysics

Solid Earth Geophysics can be subdivided into Global Geophysics or pure Geophysics and Applied Geophysics.

Who hires geophysicists?

  • Energy Companies
  • Mining Companies
  • Government Jobs
  • Engineering Consultants
  • Environmental Consultants

How Do Geophysicists “Look at” Rocks?

  • Measure properties such as density, resistivity, magnetic properties, elastic moduli, radioactivity, etc…
  • Use these properties to infer rock type / composition
  • “Indirect” approach, but offers information that is not possible to visually obtain.

Global Geophysics

Global Geophysics is the study of the whole or substantial parts of the planet. Geophysical methods may be applied to a wide range of investigations from ٣ studies of the entire earth to exploration of a localized region of the upper crust, such as plate tectonics, heat flow and paleomagnetism.

Applied Geophysics

Applied Geophysics is the study of the Earth’s crust and near surface to achieve an economic aim, or making and interpreting measurements of physical properties of the earth to determine subsurface conditions usually with an economic objectives ( e.g. discovery of fuel or mineral deposities).

Comprises the following subjects:

  1. Determination of the thickness of the crust (which is important in hydrocarbon exploration.
  2. Study of shallow structures for engineering site investigations.
  3. Exploration for ground water and for minerals and other economic resources.
  4. Trying to locate narrow mine shafts or other forms of buried cavities.
  5. The mapping of archaeological remains.
  6. Locating buried piper and cables

Engineering Geophysics

Engineering Geophysics is application of geophysical methods to the investigation of nearsurface physico-chemical phenomena which are likely to have (significant) for the management of the local environment.

  • Geophysics can be used to investigate contaminated land to locate polluted areas prior to direct observations using trail pits and boreholes. Large areas can be surveyed quickly at relatively low cost.
  • The alternative and more usual approach is to use a statistical sampling techniques, the geophysical survey is used to locate anomalous areas and there will be a higher certainly that the constructed trail pits and boreholes will yields useful results.
  • Geophysics is also being used much more extensively over landfills and other waste repositories. – Geophysics can be used to locate a corroded steel drum containing toxic chemicals. To probe for it poses the real risk of puncturing it and creating a much more significant pollution incident.
  • By using modern geomagnetic surveying methods, the drum’s position can be isolated and a careful excavation investigated to remove the offending (hurt) object without damage. Such approach is cost effective and environmentally safer.
  • Geophysics investing of the interior of the earth involve taking measurements at or near the earth’s surface that are influenced by the internal distribution of physical properties.
  • Analysis of these measurements can reveal how the physical properties of the earth’s interior vary vertically and laterally.
  • Exploration geophysics developed from the methods used in global geophysics

Useful of Geophysics

  • Adds information about the 3rd dimension.
  • Can truly “look into the Earth”
  • Gives less detailed information about much larger areas.
  • Results are often “non-unique”
  • Usually cannot give information about the past
  • Can study non-tangible things…e.g. forces

Relation between Geology and Geophysics:

Geology

It involves the study of the earth by direct observations on rocks either from surface exposures or from boreholes and the deduction of its structures, composition and historical evolution by analysis of such observations.

Geophysics

It involves the study of the inaccessible earth by means of physical measurements, usually on or above the ground surface. It also includes interpretation of the measurements in terms of subsurface structures and phenomena.

Geophysical studies are quantitative and tangible, whereas geological studies are qualitative and descriptive

Physcical Properties of Rocks

The physical properties of rocks that are most commonly utilized in geophysical investigations are:

  • Density
  • Magnetic susceptibility
  • Elasticity
  • Electrical resistively or conductivity
  • Radioactivity
  • Thermal conductivity

These properties have been used to devise geophysical methods, which are:

Geophysical Methods

The physical properties of rocks have been used to devise geophysical methods that are essential in the search for minerals, oil and gas and other geological and environmental problems.

Read More – Geophysical Methods Page

Geophysical Methods

Reference

  • Dr. El-Arabi H. Shendi ( 2007 ) Introduction of Geophysics, Suez Canal University Faculty of Science, Professor of Applied & Environmental Geophysics

Antimony

Antimony (Credit Bostock Shutterstock)
Antimony


Antimony


Antimony from Arechuybo, Chihuahua, Mexico


Antimony


Antimony


Antimony was previously known as a metal, but 1748 was defined as an element. It usually occurs in massive, leafy or granular form and it has a flaky texture that makes it shiny, silvery, bluish white and brittle. Occurring in rare, usually massive, leafy or granular form. Almost her time contains little arsenic and is found in vessels with silver, arsenic and other minerals. The antimony alloys are extremely modern. Small quantities of bile, other metals, the alloy of the accumulator plates, bullets and cables used in the coating gives the toughness and hardness. It is combined with tin and lead, antennas, babbitt metals used according to the compartments of machine beds, named friction preventing alloys. As bismuth the antimony expands slightly to solidification and makes it a round alloy metal for detailed castings.

Name: It name come from the Latin antimonium; possibly of Arabic origin; the chemical symbol from the Latin stibium, mark.

Mineral Group: Arsenic group.

Association: Silver, stibnite, allemontite, sphalerite, pyrite, galena, quartz.

Chemical Properties of Antimony

Chemical Classification Native
Chemical Composition Sb

Physical Properties of Antimony

Color Tin-white
Streak Grey
Luster Metallic
Cleavage Perfect Perfect and easy on {0001}, distinct on {1011}, imperfect on {1014} and indistinct on {1120}.
Diaphaneity Opaque
Mohs Hardness 3 – 3,5 on Mohs scale
Crystal System Trigonal, Hexagonal
Tenacity Brittle
Fracture Irregular/Uneven
Density 6.61 – 6.71 g/cm3 (Measured)    6.697 g/cm3 (Calculated)

Optical Properties of Antimony

Type Anisotropic
Color / Pleochroism Weak
Twinning On {0114}, commonly forming complex groups, fourlings, sixlings; also polysynthetic twins.

Occurrence of Antimony

It is occour in hydothermal Sb–Ag veins.

Antimony Uses and Facts

  • B.C. Articles made before Antimony until 3000 years.
  • The first published report on how to isolate antimony was made in 1540 by Vannoccio Biringuccio.
  • Antimony’s periodic symbol comes from Jons Jakob Berzelius, who uses the abbreviation stibium.
  • Antimony is stable at normal temperatures, but reacts with oxygen when heated.
  • There are four antimony allotropes known.
  • One of allotropes, metallic antimony, is stable, but the other three are metastable.
  • One of the metastatic forms is explosive antimony and produces a white smoke when drawn with a metal object.It has two stable isotopes.
  • There are also thirty-five radioactive isotopes.
  • The longest half-life of any of the radioisotopes is 2.75 years.
  • It is believed to be present in the earth’s crust at about 0.2 to 0.5 per million.
  • It is found in more than 100 different minerals.
  • It ıs sometimes found in pure form, but it is found in the most common mineral stibnite.
  • China is the largest producer of antimony, which usually accounts for 84% to 88% of supply.
  • It is listed in the British Geological Survey Risk List for its supply.
  • It is also listed as one of the twelve most critical materials by the EU as the overwhelming supply comes from outside Europe (China).
  • New antimony accumulation has not been found in China for more than a decade and the current supply is rapidly depleted.
  • The predominant uses for antimony include alloying with other metals, creation of flame-retardant products and chemical stabilizers.

Distribution

Numerous localities. In the USA, Czech Republic, Germany, Sweden, Italy, Finland, Australia, Chile, Mexico

References

Bismuth

Bismuth is a fascinating metal known for its unique properties and striking visual appeal. Among its various forms, synthetic bismuth crystals stand out due to their vibrant, rainbow-like colors. These colorful crystals are created by cooling molten bismuth in a controlled environment, allowing it to form intricate, stepped structures.

Rainbow Bismuth Crystal 

The striking iridescence of synthetic bismuth crystals results from a thin layer of oxide that forms on their surface. This layer creates interference effects with light, producing a spectrum of colors that range from pink and blue to green and gold. The process of making these crystals involves carefully managing the cooling rate and purity of the bismuth to achieve the desired aesthetic effect.

Synthetic bismuth crystals are popular in decorative items and educational demonstrations. Their dazzling appearance and complex crystal formations make them a favorite among collectors and enthusiasts, showcasing the beauty that can be achieved with this versatile metal.

Bismuth is a heavy, brittle metal with the atomic number 83 and the symbol Bi. It is known for its distinctive, iridescent appearance when oxidized, displaying hues of pink, blue, and green. The metal has a relatively low melting point of about 271.4°C (520.5°F) and is often found in nature as a compound rather than in its pure form. Bismuth is a poor conductor of electricity but is an excellent thermal conductor. It is chemically stable in air and water, though it can slowly oxidize. Its most notable physical property is its density, which is high compared to other metals, contributing to its heaviness. Bismuth is also characterized by its low toxicity compared to other heavy metals, making it a safer alternative in various applications.

Historical Use and Discovery

Bismuth has been known since antiquity, with early uses dating back to ancient civilizations. The metal was utilized in alloys and as a component in some traditional medicines. Its discovery as a distinct element, however, is credited to the German chemist Claude François Geoffroy, who in the early 18th century recognized it as a separate entity from lead, which it had previously been confused with. Geoffroy’s work laid the groundwork for understanding bismuth’s unique properties and applications. In the 19th century, with the development of modern chemistry, bismuth’s applications expanded, including its use in cosmetics, pharmaceuticals, and low-melting alloys. Its distinctive color and low toxicity further established its place in a variety of industrial and scientific applications, marking its importance in both historical and contemporary contexts.

Name: From the German weisse masse, later wismuth, white mass.

Mineral Group: Arsenic group.

Cell Data: Space Group: R3m. a = 4.546 c = 11.860 Z = 6

Association: Chalcopyrite, arsenopyrite, pyrrhotite, pyrite, cobaltite, nickeline, breithauptite, skutterudite, safflorite, bismuthinite, silver, cubanite, molybdenite, sphalerite, galena, scheelite, wolframite, calcite, barite, quartz.

Properties of Bismuth

Native Bismuth Crystal 

Physical Properties

Bismuth is a heavy, brittle metal with a silvery-white appearance that can develop an iridescent sheen when oxidized. It has a relatively high density of about 9.78 g/cm³, which is one of its notable physical characteristics. The metal is distinguished by its low thermal and electrical conductivity compared to other metals. Bismuth has a relatively low melting point of approximately 271.4°C (520.5°F), which is significantly lower than many other metals. This property makes it useful in applications requiring low-melting alloys. Additionally, bismuth exhibits a unique property in its crystal structure: when it solidifies, it expands rather than contracting, which is unusual for most metals.

Chemical Properties

Chemically, bismuth is relatively stable compared to other heavy metals. It does not react readily with air at room temperature but can form a layer of bismuth oxide (Bi₂O₃) when exposed to oxygen. Bismuth is also resistant to corrosion in water and most acids, although it does react with strong acids like hydrochloric acid to form bismuth chloride (BiCl₃). In alkaline solutions, bismuth can dissolve to form bismuthates, such as sodium bismuthate (NaBiO₃). The metal does not readily form complex compounds compared to other elements, but its compounds are often used in various applications due to their low toxicity. Bismuth compounds, such as bismuth subsalicylate, are commonly used in pharmaceuticals, including medications for digestive issues.

Optical Properties

Bismuth exhibits several interesting optical properties, although it’s not typically considered a major player in optical applications compared to other materials like silicon or various compounds used in optics. Nonetheless, here are some optical properties of bismuth:

  1. Refraction: Bismuth has a refractive index of approximately 1.9 for visible light. This means that light passing through or interacting with bismuth will be refracted, or bent, as it enters or exits the material.
  2. Reflection: Like most metals, bismuth exhibits reflectivity. However, it’s not as reflective as some other metals like silver or aluminum. The reflectivity of bismuth can vary depending on factors such as surface finish and purity.
  3. Coloration: Bismuth is known for its iridescent oxide layer that forms on its surface when exposed to air. This oxide layer can produce a range of colors, including purples, blues, greens, and yellows. This property makes bismuth crystals popular for decorative and artistic purposes.
  4. Transparency: Bismuth is generally considered opaque to visible light, meaning that light cannot pass through it. However, in thin films or certain crystal structures, bismuth can exhibit some degree of transparency, particularly in the infrared part of the spectrum.
  5. Photoluminescence: Under certain conditions, bismuth compounds can exhibit photoluminescence, emitting light when excited by photons. This property is exploited in some applications such as luminescent materials for displays and sensors.
  6. Optical Birefringence: Some bismuth-containing compounds, particularly certain crystals, exhibit optical birefringence. This means that they have different refractive indices for light polarized in different directions, resulting in double refraction.

While bismuth’s optical properties are not as extensively studied or utilized as those of some other materials, they still contribute to its unique characteristics and make it suitable for specific applications, particularly in decorative items, art, and certain scientific studies.

Identification and Classification

How to Identify Bismuth in the Field

Identifying bismuth in the field can be challenging due to its rarity and the similar appearance of its minerals to other metals. However, several methods and characteristics can help in its identification:

  1. Physical Characteristics: Bismuth metal has a distinct appearance, often exhibiting an iridescent, rainbow-like sheen due to the formation of an oxide layer. It is brittle and has a silvery-white color. Bismuth ores can be recognized by their characteristic colors and the presence of minerals like bismuthinite or bismite.
  2. Density Test: Bismuth is a heavy metal with a density of about 9.78 g/cm³. By performing a density test (e.g., measuring the weight of a sample and its volume), you can determine if the sample has a density consistent with bismuth.
  3. Chemical Tests: In the field, simple chemical tests can help identify bismuth. For example, bismuth can be tested using dilute acids to see if it reacts to form bismuth salts. Bismuth compounds often produce a white or yellow precipitate in specific reactions.
  4. Magnetic Test: Bismuth is diamagnetic, meaning it is repelled by magnetic fields. While this property is subtle and may require a strong magnet, it can be used to differentiate bismuth from ferromagnetic materials.
  5. X-ray Fluorescence (XRF): Portable XRF analyzers can provide a quick and accurate way to identify bismuth in the field. These devices measure the fluorescent X-rays emitted by a sample when exposed to a primary X-ray source, allowing for precise identification of elements.

Classification and Types of Bismuth Minerals

Bismuth minerals are classified based on their chemical composition and crystal structure. The primary bismuth minerals include:

  1. Bismuthinite (Bi₂S₃): This is one of the most important bismuth ores. It appears as metallic, grayish to black crystals and is often found in hydrothermal veins. Bismuthinite has a high density and a lead-gray color.
  2. Bismite (Bi₂O₃): Bismite is an oxide mineral that forms as an oxidation product of bismuth-containing ores. It is usually yellowish or brownish and has a relatively high density.
  3. Bismuth Copper (Cu₁₋ₓBiₓ): This mineral is a solid solution of copper and bismuth. It can be found in copper deposits and is often associated with other copper and bismuth minerals.
  4. Bismuthinite-Bismite Series: This series includes minerals that range between bismuthinite (Bi₂S₃) and bismite (Bi₂O₃), showing intermediate properties.
  5. Tetradymite (Bi₂Te₃): Although primarily a telluride, tetradymite contains bismuth and is used in thermoelectric applications. It has a metallic luster and appears as silver-gray crystals.

In summary, identifying bismuth in the field involves a combination of visual inspection, physical tests, and chemical analyses. The classification of bismuth minerals is based on their composition and crystal structure, with key minerals including bismuthinite, bismite, and tetradymite.

Formation and Occurrence

Geological Formations and Environments

Bismuth is relatively rare in the Earth’s crust and is typically found in minute quantities within certain geological formations. It primarily occurs in hydrothermal veins, which are mineral deposits formed from hot, mineral-rich fluids circulating through rocks. Bismuth can also be found in pegmatitic rocks, which are formed from the crystallization of magma in the final stages of igneous activity. Additionally, it can be associated with lead, copper, and tin ores in these mineral deposits. Bismuth is often found in compounds such as bismuthinite (Bi₂S₃), which forms from the cooling of molten rock or from mineral-rich solutions in hydrothermal environments.

Common Locations Where Bismuth is Found

Bismuth is found in several locations around the world, though it is not as abundant as other metals. Notable sources include:

  • China: One of the largest producers of bismuth, with significant deposits and mining operations.
  • Bolivia: Hosts important bismuth deposits, often associated with tin mining activities.
  • Canada: Known for its bismuth resources, particularly in the province of Quebec, where it is mined as a byproduct of other metals.
  • Mexico: Another significant producer, with bismuth found in various mineral deposits.
  • Australia: Contains bismuth in several mining operations, usually as a byproduct of gold and other metal mining.

Mining and Extraction Methods

Bismuth is typically extracted as a byproduct of mining other metals, such as lead, copper, or tin. The extraction process involves several steps:

Purification: The final step involves purifying the bismuth to meet industrial standards, ensuring it is suitable for various applications, including electronics, pharmaceuticals, and alloys.

Mining: Bismuth is mined either directly from bismuth-containing ores, such as bismuthinite, or as a byproduct of other metal ores. The ores are extracted using conventional mining methods, including underground mining or open-pit mining.

Crushing and Grinding: The mined ore is crushed and ground to liberate the bismuth minerals from the surrounding rock.

Concentration: The ground ore is processed to concentrate the bismuth-containing minerals. This often involves flotation, where chemicals are added to separate bismuth minerals from other materials.

Extraction: Bismuth is extracted from the concentrated ore using various methods. In many cases, it is recovered from lead, copper, or tin smelting processes, where it accumulates in the slag or as a residue. Specialized processes, such as solvent extraction or precipitation, may be used to separate bismuth from these mixtures.

Refining: The extracted bismuth is further refined to remove impurities. This involves processes like electrolysis or chemical reduction to obtain pure bismuth metal or bismuth compounds.

Bismuth Crystals: Rainbow Synthetic

Bismuth Crystals: Rainbow Synthetic

Bismuth crystals are known for their striking and colorful appearance, often displaying a rainbow-like iridescence. This phenomenon is due to the formation of a thin oxide layer on the surface of the crystals, which creates a spectrum of colors through interference.

Formation and Appearance

  • Crystallization: Bismuth crystals form when molten bismuth cools and solidifies. As the metal cools, it forms complex, geometric crystal structures with stepped layers or stair-like formations. These structures can be quite intricate and visually captivating.
  • Iridescence: The rainbow effect on bismuth crystals is produced by the interference of light waves reflecting off the thin oxide layer that forms on the surface of the crystal. The thickness of the oxide layer varies in different areas of the crystal, leading to different colors being reflected.

Synthetic Creation

  • Controlled Cooling: To create synthetic bismuth crystals with a rainbow effect, precise control over the cooling process is essential. This is typically done by melting bismuth and allowing it to cool slowly in a controlled environment. The cooling rate affects the formation of the crystal structures and the resulting colors.
  • Purity and Environment: The purity of the bismuth and the conditions under which it is cooled (such as temperature and the presence of other elements) can influence the appearance of the crystals. Pure bismuth and a controlled environment generally produce the most vivid and striking colors.

Applications and Uses

  • Decorative Items: Rainbow bismuth crystals are often used as decorative items due to their unique and colorful appearance. They are popular in jewelry, ornaments, and as collector’s pieces.
  • Educational Tools: These crystals are also used in educational settings to demonstrate concepts related to crystallography, light interference, and the properties of metals.

In Summary

Rainbow bismuth crystals are synthetic creations that showcase a dazzling array of colors due to the interference effects of light reflecting off a thin oxide layer. Their aesthetic appeal and unique formation process make them popular for decorative and educational purposes.

Uses and Applications

Industrial Uses

  1. Alloys: Bismuth is used in various alloys due to its low melting point and unique properties. It is a key component in low-melting alloys, which are used in applications requiring materials that melt at relatively low temperatures, such as in fire detection systems and soldering. Bismuth is also used in alloys for making metal gauges, certain types of bearings, and as a replacement for lead in some applications to reduce toxicity.
  2. Pharmaceuticals: Bismuth compounds, notably bismuth subsalicylate (Pepto-Bismol), are widely used in medicine. They are effective in treating gastrointestinal issues such as diarrhea, indigestion, and nausea. Bismuth compounds also have antibacterial properties and are used in treatments for Helicobacter pylori infection, which is linked to peptic ulcers.
  3. Cosmetics: Bismuth oxychloride is used in cosmetics, particularly in makeup products like powders and foundations. It provides a pearlescent sheen and contributes to a smooth texture, enhancing the aesthetic quality of cosmetic products.

Technological Applications

  1. Electronics: Bismuth is utilized in electronics for its unique properties. It is used in the production of certain types of semiconductors and thermoelectric materials, where its ability to conduct heat but not electricity is advantageous. Bismuth-based materials are employed in thermoelectric devices that convert temperature differences into electrical power.
  2. Nuclear Applications: Bismuth has applications in nuclear technology due to its ability to absorb neutrons. It is used in nuclear reactors as a component of control rods and as a coolant in certain reactor designs. Bismuth compounds are also utilized in the production of bismuth-based nuclear fuels and in radiation shielding materials.

In summary, bismuth’s diverse properties make it valuable across a range of industries, from medicine and cosmetics to electronics and nuclear technology. Its applications leverage its unique characteristics, such as low melting point, low toxicity, and neutron absorption, to address specific needs in various fields.

Distribution

The distribution of bismuth in nature is relatively widespread, but it tends to occur in relatively low concentrations compared to more abundant elements. Here’s a breakdown of its distribution:

  1. Earth’s Crust: Bismuth is present in the Earth’s crust at an average concentration of around 0.2 parts per million (ppm). This makes it one of the less abundant elements in the Earth’s crust.
  2. Mineral Deposits: Bismuth is typically found in association with other metal ores, particularly those of lead, copper, zinc, and silver. It occurs in various mineral forms, including bismuthinite (Bi2S3), bismite (Bi2O3), and native bismuth. These minerals are often found in hydrothermal veins, pegmatites, and other geological formations where ore deposits are formed.
  3. Global Production: The largest producers of bismuth are China, Peru, Mexico, and Canada, although smaller quantities are produced in several other countries as well. China, in particular, dominates global production, accounting for a significant portion of the world’s bismuth supply.
  4. By-Product of Other Metal Extraction: Bismuth is often obtained as a by-product of the refining of lead, copper, tin, silver, and gold ores. It is extracted from these ores through various processes such as smelting, roasting, and electrolysis.
  5. Industrial Use and Distribution: Once extracted, bismuth is utilized in various industries such as metallurgy, pharmaceuticals, cosmetics, electronics, and pyrotechnics. Its distribution in these industries depends on factors such as demand, availability, and economic considerations.
  6. Global Trade: Bismuth and its compounds are traded globally, with countries importing and exporting bismuth-based products for various applications. China, as the largest producer, also plays a significant role in the global trade of bismuth.

Overall, while bismuth is relatively rare compared to some other elements, it is still widely distributed and plays important roles in various industrial and commercial sectors around the world.

Lepidolite

Lepidolite from Itinga, Minas Gerais, Brazil
Rounded Lepidolite Crystals from Governador Valadares, Minas Gerais, Brazil

Lepidolite is Earth’s most common lithium-bearing mineral. Although typically pale lilac, specimens can also be colorless, violet, pale yellow, or gray. Lepidolite crystals may appear pseudohexagonal. The mineral is also found as botryoidal or kidneylike masses and fine- to coarse-grained, interlocking plates. Its perfect cleavage yields thin, flexible sheets. Lepidolite occurs in granitic pegmatites, where it is associated with other lithium minerals, such as beryl and topaz. The mineral is economically important as a major source of lithium, which is used to make glass and enamels. It is also a major source of the rare alkali metals rubidium and cesium.

Name: From the Greek lepidos for scale, in allusion to its micaceous structure.

Polymorphism & Series: 1M, 2M2 ; 3A polytypes common; 2M1 ; 3M2 rare; a group name.

Mineral Group: Mica group.

Crystallography: Monoclinic; prismatic. Crystals usually in small plates or prisms with hexagonal outline. Commonly in coarse- to finegrained scaly aggregates.

Association: Spodumene, elbaite, amblygonite, columbite, cassiterite, topaz, beryl, micas

Lepidolite Composition: A fluosilicate of potassium, lithium, aluminum, K2Li3Al4Si7 0 2 i(0 H,F)3. Magnesium may be present.

Diagnostic Features: Characterized chiefly by its micaceous cleavage and usually by its lilac to pink color. Muscovite may be pink, or lepidolite white, and therefore a flame test should be made to distinguish the two.

Physical properties of Lepidolite

  • Color: Lepidolite is usually pink, purple, or lilac in color, although it can also be found in other colors such as yellow, gray, and white.
  • Crystal system: Monoclinic. Lepidolite crystals are typically platy or tabular in shape.
  • Hardness: 2.5-4 on the Mohs scale, which means it is relatively soft.
  • Luster: Vitreous to pearly.
  • Streak: White.
  • Cleavage: Perfect basal cleavage in one direction, which gives it a characteristic “books” or “pages” like appearance when broken.

Chemical properties of Lepidolite

  • Composition: Lepidolite is a complex lithium aluminum silicate mineral with the chemical formula K(Li,Al,Rb)3(Al,Si)4O10(F,OH)2. It contains lithium (Li), aluminum (Al), rubidium (Rb), silicon (Si), oxygen (O), fluorine (F), and hydrogen (H).
  • Lithium content: Lepidolite is one of the primary lithium-bearing minerals, and it can contain a significant amount of lithium, usually ranging from 3% to 8% Li2O.

Unique characteristics of Lepidolite

  • Lithium content: Lepidolite is one of the primary sources of lithium, a highly valuable and critical element used in batteries, ceramics, glass, and other high-tech applications.
  • Colorful appearance: Lepidolite is known for its attractive pink, purple, and lilac colors, which make it a popular mineral among collectors and lapidary enthusiasts.
  • Cleavage: Lepidolite has perfect basal cleavage, which makes it easy to cleave into thin, flexible sheets. This property has made lepidolite historically popular as a source of mica, which was used in electrical insulators, lampshades, and other applications.
  • Radioactive properties: Some lepidolite deposits can contain trace amounts of radioactive elements, such as uranium and thorium, which can result in interesting fluorescent and phosphorescent properties when exposed to UV light.

Geology and occurrence of Lepidolite

  • Lepidolite is typically found in granite pegmatites, which are coarse-grained igneous rocks that form in the late stages of magma crystallization. These pegmatites are known for their rich concentrations of rare and valuable minerals, including lithium-bearing minerals like lepidolite.
  • Lepidolite is found in various locations around the world, including Brazil, Madagascar, the United States, Canada, Russia, and other countries. However, commercial deposits of lepidolite are relatively rare, and the majority of lepidolite is obtained as a byproduct of other mining operations.

Uses of Lepidolite

  • Lithium production: Lepidolite is an important source of lithium, which is used in the production of lithium-ion batteries for electric vehicles, energy storage systems, and portable electronics.
  • Gemstone: Lepidolite is sometimes used as a gemstone due to its attractive colors and unique appearance. It is typically cut into cabochons or used for beads, pendants, and other jewelry items.
  • Mica substitute: Historically, lepidolite has

Physical Properties of Lepidolite

Color Pink, purple, rose-red, violet-gray, yellowish, white, colorless
Streak White
Luster Sub-Vitreous, Resinous, Greasy, Pearly
Cleavage Perfect {001} perfect
Diaphaneity Transparent, Translucent
Mohs Hardness 2.5 – 4 on Mohs scale
Diagnostic Properties Cleavage
Crystal System Monoclinic
Tenacity Elastic
Fracture Micaceous
Density 2.8 – 2.9 g/cm3 (Measured)    2.83 g/cm3 (Calculated

Optical Properties of Lepidolite

Color / Pleochroism Colorless
Optical Extinction 3-10o
2V: 0° – 58°
Twinning Rare, composition plane f001g, twin axis [310].
Optic Sign Biaxial ({)
Dispersion: r > v; weak.

Lepidolite deposits

Lepidolite is typically found in pegmatite deposits, which are intrusive rocks that form in the final stages of the crystallization of magma. Pegmatites are known for their unique mineral assemblages and often contain rare and valuable minerals, including lepidolite. Lepidolite deposits can vary in size, quality, and economic viability. Here are some key aspects of lepidolite deposits:

  1. Geological formation: Lepidolite typically forms in pegmatites, which are coarse-grained igneous rocks with large crystals. Pegmatites form when the remaining liquid portion of a magma becomes enriched in rare elements and volatile components, leading to the crystallization of large, well-formed minerals, including lepidolite.
  2. Mineral association: Lepidolite is commonly associated with other lithium-bearing minerals such as spodumene, amblygonite, and petalite, as well as other pegmatite minerals like quartz, feldspar, and mica. The presence of these minerals can provide clues to the potential occurrence of lepidolite in a pegmatite deposit.
  3. Occurrence: Lepidolite deposits are found in various geological settings, including granitic or rare-metal pegmatites, greisens, and hydrothermal veins. These deposits may occur in different rock types, such as granite, gneiss, mica schist, and quartzite, depending on the local geology and tectonic history.
  4. Distribution: Lepidolite deposits are found in various countries around the world, including Brazil, Madagascar, United States, Canada, Russia, and others, as mentioned in the previous response. However, commercial deposits of lepidolite are relatively rare, and production is often limited to specific mines or regions.
  5. Mining and extraction: Lepidolite is typically extracted through traditional mining methods, including open-pit or underground mining, depending on the deposit’s depth and size. Once extracted, lepidolite may undergo beneficiation processes, such as crushing, grinding, and froth flotation, to concentrate and refine the lithium-bearing minerals.
  6. Environmental considerations: Lepidolite mining and processing may have environmental impacts, such as habitat disruption, soil erosion, and water pollution. Proper environmental management practices, including mine reclamation, waste disposal, and water treatment, are important considerations in lepidolite mining operations to minimize their environmental footprint.

It’s important to note that the geology, occurrence, and extraction methods of lepidolite may vary depending on the specific deposit and location. Detailed geological and technical studies are typically conducted to assess the economic viability and environmental impact of lepidolite deposits before commercial extraction takes place.

Distribution

Lepidolite is found in various locations around the world, although commercial deposits are relatively rare. Some of the major regions where lepidolite is known to occur include:

  1. Brazil: Lepidolite deposits are found in several states in Brazil, including Minas Gerais, Rio Grande do Norte, and Paraíba. Brazilian lepidolite is known for its beautiful pink and lilac colors and is often used as a gemstone or lapidary material.
  2. Madagascar: Madagascar is known for its rich pegmatite deposits, which often contain lepidolite. The Ambatofinandrahana and Antsirabe regions in Madagascar are known for their lepidolite deposits.
  3. United States: Lepidolite can be found in several states in the United States, including California, Colorado, Maine, New Mexico, and South Dakota. Some of the famous pegmatite mines in the U.S., such as the Pala District in California and the Black Hills in South Dakota, have produced notable specimens of lepidolite.
  4. Canada: Lepidolite has been found in pegmatites in various provinces of Canada, including Ontario, Manitoba, and Quebec. However, commercial deposits are relatively limited.
  5. Russia: Lepidolite deposits have been reported in some regions of Russia, including the Murmansk Oblast in the Kola Peninsula and the Transbaikal region in Eastern Siberia.
  6. Other countries: Lepidolite has also been found in smaller quantities in other countries, including Argentina, China, Czech Republic, Germany, Zimbabwe, and Namibia.

It’s worth noting that lepidolite deposits can vary significantly in size, quality, and economic viability. Commercial exploitation of lepidolite deposits may depend on factors such as lithium demand, market prices, geological and economic considerations, and environmental regulations.

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Dana, J. D. (1864). Manual of Mineralogy… Wiley.
  • Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mindat.org. (2019). Lepidolite: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].

Iron

Five percent of Earth’s crust is made up of iron. Native iron is rare in the crust and is invariably alloyed with nickel. Low-nickel iron (up to 7.5 percent nickel) is called kamacite, and high-nickel iron (up to 50 percent nickel) is called taenite. Both crystallize in the cubic system. A third form of iron-nickel, mainly found in meteorites and crystallizing in the tetragonal system, is called tetrataenite. All three forms are generally found either as disseminated grains or as rounded masses. Kamacite is the major component of most iron meteorites. It is found in most chondritic meteorites, and occurs as microscopic grains in some lunar rocks. Taenite and tetrataenite are mainly found in meteorites, often intergrown with kamacite. It is also plentiful in the Sun and other stars.

Name: An Old English word for the metal; the chemical symbol from the Latin ferrum.

Association: Pyrite, magnetite, troilite, w¨ustite, cohenite

Iron Ore Lumps
Iron Ore Mining
Iron Ore

Chemical Properties of Iron

Chemical Classification Native
Chemical Composition Fe

Physical Properties of Iron

Color Iron-black
Streak Grey
Luster Metallic
Cleavage Imperfect/Fair On {001}
Diaphaneity Opaque
Mohs Hardness 4½ on Mohs scale
Diagnostic Properties Specific gravity, color
Crystal System Cubic
Tenacity Malleable
Fracture Hackly
Density 7.3 – 7.87 g/cm3 (Measured)    7.874 g/cm3 (Calculated)
Parting On (112)

Optical Properties of Iron

Type Isometric
Colour in reflected light: White
Twinning (111), in lamellar masses also {112}.

Occurrence

Rare in igneous rocks, especially basalts; in carbonaceous sediments; in volcanic fumaroles; and in petrified wood, mixed with “limonite” and organic matter.

Uses Area

Near the producer of iron produced in the world is used in steel making. Because It alone is the successful strong depot.

Tungsten, manganese, nickel, vanadium, chrome etc. It is used in many areas such as construction and automobile.

Powder iron: used in metallurgy products, magnets, high frequency nuclei, automobile parts, catalysts.

The stainless steel is very resistant to corrosion. It contains at least 10.5% chromium. Other metals such as nickel, molybdenum, titanium and copper are added to increase the strength and workability. It is used in architecture, beds, cutlery, surgical instruments and jewelry.

Cast iron contains 3-5% carbon. It is used for pipes, valves and pumps. It’s not as hard as steel, but it’s cheap. Magnets can be made of ıts and its alloys and compounds.

It catalysts to produce ammonia in news processing and to convert syngas (hydrogen and carbon monoxide) into liquid fuels in Fischer-Tropsch process.

Radioactive iron (59): tracer in medicine, biochemical and metallurgical studies. Iron blue: paints, printing inks, plastics, cosmetics (eye shadow), painter colors, laundry blue, paper paint, fertilizer component, baked enamel coatings for automobiles and household appliances, industrial surfaces. Black iron oxide: as pigment, in polishing compounds, in metallurgy, in medicine, in magnetic inks, in ferrite for the electronics industry.

Biological Factor of Iron

It is an important element for all life forms and is not toxic. The average person contains about 4 grams of iron. Most of them in hemoglobin, in the blood. Hemoglobin carries oxygen from our lungs to the cells needed for tissue respiration.

People need 10 to 18 milligrams of iron every day. Iron deficiency causes anemia. Foods such as liver, kidney, molasses, brewer’s yeast, cocoa and licorice contain a lot of iron.

Iron Facts

  • Atomic number (number of protons in the nucleus): 26
  • Atomic symbol (Periodic Table of the Elements): Fe
  • Atomic weight (average mass of atom): 55.845
  • Density: 7.874 grams per cubic centimeter
  • Phase at room temperature: Solid
  • Melting point: 2,800.4 degrees Fahrenheit (1,538 degrees Celsius)
  • Boiling point: 5,181,8 F (2,861 C)
  • Isotope number (different number of neutrons containing the same element): (including how many stable isotopes): 33 Stable isotopes: 4
  • The most common isotopes: Iron-56 (natural abundance: 91.754 percent)

Distribution

  • In Greenland, at Fortune Bay, Mellemfjord, Asuk, and elsewhere on the west coast; on Disko Island, near Uivfaq and Kitdlit.
  • From Ben Bhreck, Scotland.
  • At B¨uhl, near Weimar, Hesse, Germany. In Poland, near Rouno, Wolyn district.
  • In Russia, at Grushersk, in the Don district; from the Hatanga region, Siberia; in the Huntukungskii massif, Krasnoyarsk Kray; and on the Tolbachik fissure volcano, Kamchatka Peninsula.
  • In the USA, at Cameron, Clinton Co., Missouri; and near New Brunswick, Somerset Co., New Jersey.
  • In Canada, in Ontario, from Cameron Township, Nipissing district, and on St. Joseph Island, Lake Huron. Noted in small amounts at a number of additional localities.

References

Augite

The most common pyroxene, augite is named after the Greek word augites, which means “brightness”—a reference to its occasional shiny appearance. Most augite has a dull, dark green, brown, or black finish. Augite occurs chiefly as short, thick, prismatic crystals with a square or octagonal cross section and sometimes as large, cleavable masses. It occurs in a solid-solution series in which diopside and hedenbergite are the end-members. Augite is common in silica-poor rocks and various other dark-colored igneous rocks, as well as igneous rocks of intermediate silica content. It also occurs in some metamorphic rocks formed at high temperatures (1,065°F/575°C or above). Augite is a common constituent of lunar basalts and some meteorites. Notable crystal localities are in Germany, the Czech Republic, Italy, Russia, Japan, Mexico, Canada, and USA. Because it is difficult to distinguish between augite, diopside, and hedenbergite in hand specimens, all pyroxenes are often identified as augite.

Name: From the Greek for luster, apparently based on the appearance of its cleavage surface.

Mineral Group: Pyroxene group.

Association: Orthoclase, sanidine, labradorite, olivine, leucite, amphibole, pyroxene

Chemical Properties of Augite

Chemical Classification Inosilicates
Chemical Composition (CaxMgyFez)(Mgy1Fez1)Si2O6

Physical Properties of Augite

Color Brown-green, black, green-black, brown, purplish brown
Streak Greenish gray, light to dark brown
Luster Vitreous
Cleavage Distinct/Good Good on {110}
Diaphaneity Translucent, Opaque
Mohs Hardness 5½ – 6 on Mohs scale
Crystal System Monoclinic
Tenacity Brittle
Parting on {100} and {010}
Fracture Irregular/Uneven, Sub-Conchoidal
Density 3.19 – 3.56 g/cm3 (Measured)    3.31 g/cm3 (Calculated)

Optical Properties of Augite

Augite under the Microscope
Type Anisotropic
Crystal Habit Grains often anhedral; May be granular, massive, columnar or lamellar
Color / Pleochroism x=pale green or bluish green y=pale greenish, brown, green or bluish green z=pale brownish green, green or yellow-green
Optical Extinction Z : c = 35°-48°
2V: Measured: 40° to 52°, Calculated: 48° to 68°
RI values: nα = 1.680 – 1.735 nβ = 1.684 – 1.741 nγ = 1.706 – 1.774
Twinning Commonly displays simple and lamellar twinning on {100} and {001}; They may combine to form a herringbone pattern. Exsolution lamellae may be present.
Optic Sign Biaxial (+)
Birefringence δ = 0.026 – 0.039
Relief High
Dispersion: r > v weak to distinct

Occurrence

Essential in mafic igneous rocks, basalt, gabbro; common in ultramafic rocks; in some high-grade metamorphic rocks and metamorphosed iron formations.

Uses Area

Augite is a mineral of interest to geologists, and collectors. While it has little to no industrial value, the presence and development of augite may help tell scientists and geologists about Earth’s history in certain regions.

Distribution

Widespread; only a few classic localities, much studied or providing

  • From Arendal, Norway.
  • In Italy, from Vesuvius, Campania; around Frascati, Alban Hills, Lazio; on Mt. Monzoni, Val di Fassa, Trentino-Alto Adige; at Traversella, Piedmont; and on Mt. Etna, Sicily. Around the Laacher See, Eifel district, On the Azores and Cape Verde Islands.
  • In Canada, from Renfrew and Haliburton Cos., Ontario; at Otter Lake, Pontiac Co., Quebec; and many other localities.
  • In the USA, from Franklin and Sterling Hill, Ogdensburg, Sussex Co., New Jersey; and at Diana, Lewis Co., and Fine, St. Lawrence Co., New York.
  • From Tomik, Gilgit district, Pakistan.
  • At Kangan, Andhra Pradesh, India.

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mindat.org. (2019). Halite: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
  • Smith.edu. (2019). Geosciences | Smith College. [online] Available at: https://www.smith.edu/academics/geosciences [Accessed 15 Mar. 2019].

Glaucophane

The Glaucophane mineral is named after two Greek words: glaukos, which means “bluish green”; and phainesthai, which means “to appear.” Specimens can be gray, lavender blue, or bluish black. Crystals are slender, often lathlike prisms, with lengthwise striations. Twinning is common. Glaucophane can also be massive, fibrous, or granular. When iron replaces the magnesium in its structure, it is known as ferroglaucophane. Glaucophane occurs in schists formed by high-pressure metamorphism of sodium-rich sediments at low temperatures (up to 400°F/200°C) or by the introduction of sodium into the process. Glaucophane is often accompanied by jadeite, epidote, almandine, and chlorite. It is one of the minerals that are referred to as asbestos. Glaucophane and its associated minerals are known as the glaucophane metamorphic facies. The presence of these minerals indicates the range of temperatures and pressures under which metamorphism occurs.

Name: From the Greek for bluish green and to appear.

Polymorphism & Series: Forms a series with ferroglaucophane.

Mineral Group: Amphibole (alkali) group: Fe 2+=(Fe 2+ + Mg) < 0.5; Fe 3+=(Fe 3+ + Al vi ) < 0.3; (Na + K)A < 0.5; NaB ¸ 1.34.

Association: Crossite, chlorite, epidote, pumpellyite, lawsonite, omphacite, jadeite, actinolite, barroisite, cummingtonite, aragonite.

Chemical Properties of Glaucophane

Chemical Classification Inosilicates
Chemical Composition Na2(Mg3Al2)Si8O22(OH)

Physical Properties of Glaucophane

Color Grey to lavender-blue.
Streak Pale grey to bluish-grey.
Luster Vitreous
Cleavage Good on [110] and on [001]
Diaphaneity Translucent
Mohs Hardness 5 – 6 on Mohs scale
Diagnostic Properties Distinguished from other amphiboles by distinct blue color in hand sample. Blue pleochroism in thin section/grain mount distinguishes from other amphiboles. Glaucophane has length slow, riebeckite length fast. Darkest when c-axis parallel to vibration direction of lower polarizer (blue tourmaline is darkest w/ c-axis perpendicular to vibration direction of polarizer). There is no twinning in glaucophane. Glaucophane also has a parallel extinction when viewed under cross polars.
Crystal System Monoclinic
Fracture Brittle – conchoidal
Density 3 – 3.15

Optical Properties of Glaucophane

Color / Pleochroism Lavender blue, blue, dark blue, gray or black. Distinct pleochroism: X= colorless, pale blue, yellow; Y= lavender-blue, bluish green; Z= blue, greenish blue, violet
Optical Extinction  
2V: Measured: 10° to 80°, Calculated: 62° to 84°
RI values: nα = 1.606 – 1.637 nβ = 1.615 – 1.650 nγ = 1.627 – 1.655
Optic Sign Biaxial (-)
Birefringence δ = 0.021
Relief Moderate
Dispersion: strong

Occurrence

Characteristic of the blueschist facies, in former subduction zones in mountain belts; in the greenschist facies and in eclogites that have undergone retrograde metamorphism.

Distribution

Widespread in some mountain belts. On Syra Island, Cyclades Islands, Greece. At numerous sites in the California Coast Ranges, as on the Tiburon Peninsula and at Vonsen Ranch, Marin Co., at Glaucophane Ridge, Panoche Valley, San Benito Co., and near Valley Ford, Sonoma Co.; in the Kodiak Islands, Alaska, USA. At St. Marcel, Val d’Aosta, and Piollore (Biella), Piedmont, Italy. On Anglesey, Wales. In Japan, at Ubuzan, Aichi Prefecture, and Otakiyama, Tokushima Prefecture.

References

Anthophyllite

The name anthophyllite comes from the Latin word anthophyllum, which means “clove”—a reference to the mineral’s clove-brown to dark brown color. Specimens can also be pale green, gray, or white. Anthophyllite is usually found in columnar to fibrous masses. Single crystals are uncommon; when found, they are prismatic and usually unterminated. The iron and magnesium content in anthophyllite is variable. The mineral is called ferroanthophyllite when it is iron-rich, sodium-anthophyllite when sodium is present, and magnesioanthophyllite when magnesium is dominant. Titanium and manganese may also be present in the anthophyllite structure. Anthophyllite forms by the regional metamorphism of iron- and magnesium-rich rocks, especially silica-poor igneous rocks. It is an important component of some gneisses and crystalline schists and is found worldwide. Anthophyllite is one of several minerals referred to as asbestos.

Name: From the Latin anthophyllum, meaning clove, in allusion to the mineral’s color.

Association: Cordierite, talc, chlorite, sillimanite, mica, olivine, \hornblende,” gedrite, magnesio-cummingtonite, garnet, staurolite, plagioclase.

Polymorphism & Series: Forms a series with magnesio-anthophyllite and ferro-anthophyllite.

 Mineral Group: Amphibole (Fe{Mn{Mg) group: 0.1 Mg=(Mg + Fe 2+) 0.89; (Ca + Na)B < 1.34; Li < 1.0; Si ¸ 7.0.

Anthophyllite from Bastnäs mines, Riddarhyttan, Västmanland
Anthophyllite from New England quarry, Yealmpton, Devon
Anthophyllite from Wissahickon Creek, Fairmount Park, Philadelphia, Pennsylvania
Antofillit-(Anthophyllite)-Mineral

Chemical Properties of Anthophyllite

Chemical Classification Inosilicates
Chemical Composition (Mg,Fe)7Si8O22(OH)2

Physical Properties of Anthophyllite

Color White, greenish grey, green, clove brown, or brownish gree
Streak White to greyish-white.
Luster Vitreous, Pearly
Cleavage Perfect Perfect on {210}, imperfect on {010}, {100}
Diaphaneity Transparent, Translucent
Mohs Hardness 5½ – 6 on Mohs scale
Tenacity Brittle; elastic when fibrous
Diagnostic Properties Characterized by clove brown color, but unless in crystals, difficult to distinguish from other amphiboles without optical and/or X-ray tests
Crystal System Orthorhombic
Fracture Conchoidal
Density 2.85 – 3.57 g/cm3 (Measured)    3.67 g/cm3 (Calculated)

Optical Properties of Anthophyllite

Anthophyllite in thin section 
Optic Sign Biaxial (+)
Birefringence δ = 0.017 – 0.023
Relief Moderate
2V: Measured: 57° to 90°, Calculated: 82° to 90°
Dispersion r > v or r < v

Occurrence

From medium- or high-grade metamorphism, in amphibolites, gneisses, metaquartzites, iron formations, granulites, and schists derived from argillaceous sediments, ultrama¯c, or ma¯c igneous rocks; a retrograde reaction product.

Distribution

From Kongsberg and Snarum, Norway. At Schneeberg, Saxony, Germany. From Norberg, Sweden. At He·rmanov, Czech Republic. In Greenland, from Fisken½sset. In the USA, from Chester¯eld, Hampshire Co., Massachusetts; the Carleton talc mine, near Chester, Windsor Co., Vermont; near Media, Delaware Co., Pennsylvania; the Day Book deposit, near Spruce Pine, Mitchell Co., North Carolina; in California, at the Winchester quarry, Riverside Co., and near Co®ee Creek, Carrville, Trinity Co.; in the Copper Queen mine, Prairie Divide, Park Co., Colorado. From Munglinup, Western Australia.

References

Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.

Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].

Mindat.org. (2019). Anthophyllite: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].

Platinum

Platinum is a precious metal that is known for its rarity, beauty, and various industrial applications. It is a chemical element with the symbol Pt and atomic number 78 on the periodic table.

Introduction: Platinum is typically found in nature as a rare mineral, but it is more commonly obtained as a byproduct of other metal mining, particularly from ores containing nickel and copper. It is a dense, malleable, and highly corrosion-resistant metal, making it valuable for various purposes, including jewelry, catalytic converters in automobiles, and industrial applications. Its name “platinum” is derived from the Spanish term “platina,” meaning “little silver,” because early Spanish explorers often encountered platinum alongside silver deposits and initially considered it a nuisance.

Definition as a Mineral: In a geological context, it is considered a mineral when it naturally occurs in the Earth’s crust. It usually forms as small, nugget-like grains or irregular grains within certain types of rocks and ore deposits. Platinum minerals are commonly associated with nickel and copper ores, and the primary mineral source for it is often the mineral sperrylite (PtAs2). Sperrylite is a platinum arsenide mineral that is one of the few naturally occurring minerals containing platinum as its primary component.

Platinum can also occur as an alloy with other elements in nature. For example, native platinum, which consists mainly of platinum (Pt) and minor impurities, is a rare occurrence. It is usually found in alluvial deposits, often associated with other heavy minerals like gold and palladium.

It’s important to note that the vast majority of the world’s platinum production comes from primary sources (ores rich in platinum-group elements), rather than from native platinum. Extracting platinum from its ores and processing it is a complex and energy-intensive industrial process. It is highly prized for its luster, durability, and resistance to tarnish, making it a valuable material in various industries and for decorative purposes.

Cell Data: Space Group: Fm3m. a = 3.9231 Z = 4

Name: From the Spanish platina, diminutive of plata, silver.

Association: Pt–Fe alloys, chalcopyrite, chromite, magnetite

Properties of Platinum

Platinum Crystals from Russia

Platinum is a precious metal that is known for its rarity, beauty, and various industrial applications. It is a chemical element with the symbol Pt and atomic number 78 on the periodic table. Here’s an introduction and definition of platinum as a mineral:

Introduction: Platinum is typically found in nature as a rare mineral, but it is more commonly obtained as a byproduct of other metal mining, particularly from ores containing nickel and copper. It is a dense, malleable, and highly corrosion-resistant metal, making it valuable for various purposes, including jewelry, catalytic converters in automobiles, and industrial applications. Its name “platinum” is derived from the Spanish term “platina,” meaning “little silver,” because early Spanish explorers often encountered platinum alongside silver deposits and initially considered it a nuisance.

Definition as a Mineral: In a geological context, platinum is considered a mineral when it naturally occurs in the Earth’s crust. It usually forms as small, nugget-like grains or irregular grains within certain types of rocks and ore deposits. Platinum minerals are commonly associated with nickel and copper ores, and the primary mineral source for platinum is often the mineral sperrylite (PtAs2). Sperrylite is a platinum arsenide mineral that is one of the few naturally occurring minerals containing platinum as its primary component.

Platinum can also occur as an alloy with other elements in nature. For example, native platinum, which consists mainly of platinum (Pt) and minor impurities, is a rare occurrence. It is usually found in alluvial deposits, often associated with other heavy minerals like gold and palladium.

It’s important to note that the vast majority of the world’s platinum production comes from primary sources (ores rich in platinum-group elements), rather than from native platinum. Extracting platinum from its ores and processing it is a complex and energy-intensive industrial process. Platinum is highly prized for its luster, durability, and resistance to tarnish, making it a valuable material in various industries and for decorative purposes.

Physical, Chemical and Optical Properties of Platinum

Platinum is a unique and valuable metal with a range of physical, chemical, and optical properties that make it suitable for various industrial, scientific, and decorative applications. Here are some of the key properties of platinum:

Physical Properties:

  1. Density: Platinum is a very dense metal, with a density of approximately 21.45 grams per cubic centimeter (g/cm³). This high density makes it heavy and gives it a substantial feeling.
  2. Melting Point: Platinum has a very high melting point of around 1,768 degrees Celsius (3,214 degrees Fahrenheit). This high melting point makes it suitable for high-temperature applications.
  3. Boiling Point: Platinum’s boiling point is even higher, at around 3,827 degrees Celsius (6,920 degrees Fahrenheit), making it resistant to vaporization at high temperatures.
  4. Malleability and Ductility: Platinum is a highly malleable and ductile metal, which means it can be easily shaped, rolled, and drawn into various forms, making it ideal for jewelry and industrial processes.
  5. Hardness: Platinum is a relatively soft metal compared to some other precious metals, but it is still harder than most base metals. Its hardness can be improved by alloying with other elements.
  6. Color: Platinum has a distinctive silvery-white color, which contributes to its desirability for jewelry and other decorative purposes.

Chemical Properties:

  1. Chemical Inertness: One of the most notable chemical properties of platinum is its resistance to corrosion and chemical reactions. It is highly inert and does not readily react with oxygen, water, or most common acids, making it an excellent choice for use in corrosive environments.
  2. Catalytic Properties: Platinum is a highly effective catalyst for various chemical reactions. Its surface can facilitate reactions that are important in industries such as automotive (in catalytic converters) and chemical production.
  3. Alloying: Platinum can be easily alloyed with other metals, such as iridium, palladium, and rhodium, to enhance its properties and create alloys with specific characteristics.

Optical Properties:

  1. Luster: Platinum has a brilliant metallic luster, which adds to its visual appeal, making it a sought-after metal for jewelry and other ornamental purposes.
  2. Reflectivity: Platinum is highly reflective, both in the visible and infrared spectra. This property is essential in applications like laboratory equipment and mirrors.
  3. Transparency: Platinum is not transparent, as it is a dense metal that does not allow the passage of light. It is often used in the form of thin foils for some optical applications.

These properties make platinum a versatile and valuable material for various applications, ranging from jewelry and decorative items to industrial catalysts, laboratory equipment, and high-temperature engineering. Its exceptional resistance to corrosion and tarnish, coupled with its unique catalytic properties, make it an indispensable element in many technological and scientific fields.

Formation and Occurrence of Platinum

Platinum is a relatively rare and precious metal that is formed through natural geological processes. It is found in various geological settings as part of specific ore deposits. The formation and occurrence of platinum are influenced by its association with other elements, primarily nickel and copper. Here is an overview of how platinum is formed and where it is typically found:

Formation of Platinum:

  1. Magmatic Processes: The primary source of it is magmatic ore deposits, which originate from the cooling and solidification of molten rock (magma) deep within the Earth’s mantle and crust. These deposits are associated with igneous rocks and are known as “platinum group element (PGE) deposits.” PGEs, including platinum, palladium, and rhodium, are often found together in these deposits.
  2. Crystallization: During the cooling of magmas, minerals rich in platinum and other PGEs crystallize from the molten material. These minerals may include sulfides like sperrylite (PtAs2), cooperite (PtS), and braggite (Pt, Pd, Ni)S. Platinum is often found in combination with these minerals.

Occurrence of Platinum:

  1. Layered Intrusions: One of the most significant geological settings for platinum deposits is in layered intrusions, which are large, layered igneous rock formations that often extend deep within the Earth’s crust. These intrusions are typically associated with ultramafic and mafic rock types and are characterized by the presence of platinum-rich sulfide minerals.
  2. Ophiolite Complexes: Platinum deposits can also be found in ophiolite complexes, which are fragments of oceanic crust and upper mantle rocks that have been thrust onto continental landmasses. These complexes can contain platinum-bearing ore deposits, particularly in association with chromite ores.
  3. Alluvial Deposits: In some cases, platinum is eroded from primary sources like layered intrusions and transported by rivers and streams. Over time, it can accumulate in alluvial deposits, often alongside other heavy minerals such as gold. This is where native platinum, which is nearly pure platinum metal, is occasionally found.
  4. Residues from Industrial Processes: Platinum is sometimes a byproduct of various industrial processes, particularly those involving the refining of nickel and copper ores. In such cases, platinum is extracted from the residues of these processes.

It’s important to note that it is relatively rare in the Earth’s crust, and its mining and extraction can be economically challenging due to its low natural abundance. The largest producers of platinum are typically South Africa, Russia, and Zimbabwe, where significant deposits of platinum group elements are found.

The exploration and extraction of platinum are carried out using a combination of geological surveys, drilling, and mining techniques to locate and extract the metal from its primary sources, making it an essential resource for various industrial applications, including catalytic converters in automobiles and the production of high-value jewelry.

Application and Uses Areas

Platinum has a wide range of applications and is used in various industries due to its unique combination of physical and chemical properties. Some of its primary application areas and uses include:

  1. Automotive Industry:
    • Catalytic Converters: It is a key component in catalytic converters, which are used to reduce harmful emissions from vehicles by converting pollutants like carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) into less harmful substances. Palladium and rhodium, also part of the platinum group metals (PGMs), are used in catalytic converters alongside platinum.
  2. Jewelry and Ornaments:
    • Precious Jewelry: Platinum is highly prized in the jewelry industry for its lustrous appearance, durability, and rarity. It is often used to make engagement rings, wedding bands, necklaces, and other fine jewelry.
  3. Electronics:
    • Electrodes: Platinum’s excellent electrical conductivity, resistance to corrosion, and stability make it a valuable material for various electronic components, including electrodes used in devices like sensors, pacemakers, and high-precision measuring instruments.
  4. Medical and Dental Applications:
    • Implants: Platinum is used in medical implants like pacemakers and stents due to its biocompatibility and resistance to corrosion within the human body.
    • Dental Restorations: Platinum can be found in dental alloys used for restorations such as crowns, bridges, and dental braces.
  5. Industrial Processes:
    • Chemical Industry: Platinum serves as a catalyst in numerous chemical reactions, including the production of chemicals, pharmaceuticals, and petrochemicals.
    • Oil Refining: Platinum is used in the petroleum industry to catalyze various refining processes, such as the removal of impurities from crude oil and the production of high-octane gasoline.
  6. Glass Manufacturing:
    • Glass Fiber Production: It is used in the production of high-quality glass fibers used in fiber optics and telecommunications.
  7. Aerospace and Space Exploration:
    • Rocket Engines: Platinum’s high melting point and resistance to high temperatures make it suitable for use in rocket engines and aerospace components.
  8. Renewable Energy:
    • Fuel Cells: It is used as a catalyst in hydrogen fuel cells, which can be employed for clean and efficient energy generation.
    • Solar Cells: It is used in the production of solar cells, where it helps improve the efficiency and longevity of the cells.
  9. Laboratory and Scientific Equipment:
    • Crucibles: Platinum crucibles are used for high-temperature and high-purity applications in laboratories.
    • Thermocouples: It is used in thermocouples for precise temperature measurement.
  10. Currency and Bullion:
    • Some countries, such as the Isle of Man and the United Kingdom, have used platinum coins as a form of currency.
    • Platinum bullion bars and coins are also traded as a form of investment.

It’s important to note that platinum is a relatively expensive and rare metal, which can influence its application in various industries. Additionally, the high cost of extraction and refining plays a role in determining the availability and usage of platinum in different sectors. Its unique properties, especially its catalytic abilities and resistance to corrosion, make it invaluable in applications where other materials fall short.

Mining Sources and Distribution

Mogolokwena Platinum Mine, South Africa

Platinum is primarily mined from specific geological sources and is not evenly distributed around the world. The majority of platinum production comes from a few key regions with significant platinum deposits. Here are some of the main mining sources and the distribution of platinum:

1. South Africa:

  • South Africa is the world’s largest producer of platinum, accounting for a substantial portion of the global supply. The Bushveld Complex in South Africa is a vast geological formation that contains numerous platinum group element (PGE) deposits, including platinum, palladium, rhodium, and others. Mines in this region, such as the Rustenburg and Mogalakwena mines, are among the most productive in the world.

2. Russia:

  • Russia is the second-largest producer of platinum globally. The majority of Russian platinum production comes from the Norilsk-Talnakh region in Siberia. The deposits here are also part of large PGE-rich intrusions.

3. Zimbabwe:

  • Zimbabwe is another significant producer of platinum. Mines like the Great Dyke project have contributed to Zimbabwe’s growing role in global platinum production.

4. Canada:

  • Canada is known for its platinum production from the Lac des Iles Mine in Ontario. Canadian platinum mining primarily extracts nickel along with platinum group elements.

5. United States:

  • The Stillwater Complex in Montana, United States, is a notable source of platinum and palladium. It is one of the few locations outside of South Africa and Russia with economically viable platinum mining.

6. Other Countries:

  • Several other countries also produce platinum to a lesser extent, including Australia, Colombia, and Botswana, among others.

It’s important to note that while it is found in various parts of the world, the largest and most productive deposits are concentrated in just a few regions. Additionally, platinum is often produced as a byproduct of other mining operations, particularly those focused on nickel and copper. The platinum group elements (PGEs), which include platinum, palladium, rhodium, iridium, ruthenium, and osmium, are often found together in these deposits.

The mining and extraction of platinum are capital-intensive processes, and the metal’s high market value reflects the challenges and costs associated with its production. Additionally, the availability of platinum can be influenced by factors such as political stability, economic conditions, and environmental regulations in the countries where it is mined. These factors can impact the global distribution of platinum and its supply to various industries, including the automotive and jewelry sectors.

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mindat.org. (2019). Platinum: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].

Anorthoclase

Anorthoclase minerals is member of the sodium- and potassium-rich feldspar group takes its name from the Greek word anorthos, which means “not straight”—a reference to its oblique cleavage. Anorthoclase is colorless, white, cream, pink, pale yellow, gray, or green. Its crystals are prismatic or tabular and are often multiply twinned. Anorthoclase crystals can show two sets of fine lines at right angles to each other like microcline, but the lines are much finer. Specimens can also be massive or granular. Anorthoclase forms in sodium-rich igneous zones. It commonly occurs with ilmenite, apatite, and augite. Much anorthoclase exhibits a gold, bluish, or greenish schiller effect, making it one of several feldspars known as moonstone when cut en cabochon. A type of the igneous rock syenite called larvikite has large schillerized crystals of anorthoclase and is highly prized as an ornamental stone. Anorthoclase is widespread, but fine examples come from Cripple Creek, Colorado, USA; Larvik, Norway; and Fife, Scotland.

Name: From the Greek for oblique and fracture, descriptive of the cleavage.

Mineral Group: Feldspar (alkali) group; intermediate between low sanidine and high albite.

Chemical Properties of Anorthoclase

Chemical Classification Silicates Minerals
Chemical Composition (Na,K)AlSi3O8

Physical Properties of Anorthoclase

Color White, colourless, greyish pink
Streak White
Luster Vitreous to pearly on cleavage planes
Cleavage Perfect
Diaphaneity Transparent
Mohs Hardness 6 – 6½ on Mohs scale
Specific Gravity 2.57 – 2.60
Crystal System Triclinic
Tenacity Brittle
Fracture Uneven

Optical Properties of Anorthoclase

Type Anistropic
Color / Pleochroism Colorless
Twinning Polysynthetic twinning produces a grid pattern on [100]
Optic Sign Biaxial (-)
Birefringence δ = 0.008
Relief Low

Occurrence

In high-temperature sodic volcanic and hypabyssal rocks.

Association

Typically in a fine-grained groundmass or weathered out as loose crystals

Distribution

Rather abundant worldwide. Some localities for well-characterized material include:

  • on Pantelleria and Ustica Islands, Italy.
  • At Larvik, Norway.
  • From Berkum, North Rhine-Westphalia, Germany.
  • On Grande Caldeira Island, Azores.
  • At Ropp, Nigeria.
  • On Mt. Kenya, Kenya.
  • From Kilimanjaro, Tanzania. At Chilposan, near Minchon, North Korea.
  • From Ogaya, Toyama Prefecture, and Madarajima, Saga Prefecture, Japan.
  • At Kakanui, New Zealand.
  • From Mt. Anakie and Mt. Franklin,
  • Daylesford, Victoria, Australia.
  • Large crystals from Mt. Erebus, Ross Island, Antarctica.
  • At Boron, Kern Co., California, USA.

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mindat.org. (2019). Anorthoclase: Mineral information, data and localities.. [online] Available at: https://www.mindat.org

Microcline

Microcline grain in centre showing its distinctive cross-hatched twinning.

Microcline is one of the most common feldspar minerals. It can be colorless, white, cream to pale yellow, salmon pink to red, or bright green to blue-green. Microcline forms short prismatic or tabular crystals that are often of considerable size: single crystals can weigh several tons and reach yards in length. Crystals are often multiply twinned, with two sets of fine lines at right angles to each other. This gives a “plaid” effect that is unique to microcline among the feldspars. Microcline can also be massive. The mineral occurs in feldspar-rich rocks, such as granite, syenite, and granodiorite. It is found in granite pegmatites and in metamorphic rocks, such as gneisses and schists.

Polymorphism & Series: Dimorphous with orthoclase.

Mineral Group: Feldspar (alkali) group; (Si,Al) is completely ordered in low microcline.

Chemical Properties of Microcline

Chemical Classification Silicate
Chemical Composition K(AlSi3O8)

Physical Properties of Microcline

Color White, grey, greyish yellow, yellowish, tan, salmon-pink, bluish green, green.
Streak White
Luster Vitreous
Cleavage Perfect on [001], good on [010]
Diaphaneity Transparent, Translucent
Mohs Hardness 6 – 6½ on Mohs scale
Specific Gravity 2.54 – 2.57
Crystal System Triclinic
Tenacity Brittle
Parting on {100}{110}{110}{201}
Fracture Irregular/Uneven
Density 2.54 – 2.57 g/cm3 (Measured)    2.56 g/cm3 (Calculated)

Optical Properties of Microcline

Microcline grain in centre showing its distinctive cross-hatched twinning.
Type Anisotropic
Optical Extinction Inclined extinction to cleavage
Twinning Carlsbad, Baveno, Manebach, polysynthetic on albite and pericline laws.
Optic Sign Biaxial (-)
Birefringence δ = 0.007 – 0.010
Relief Low

Occurrence

Common in plutonic felsic rocks, as granites, granite pegmatites, syenites; in metamorphic rocks of the greenschist and amphibolite facies; in hydrothermal veins. A detrital component in sedimentary rocks and as authigenic overgrowths.

Uses Areas

  • The most important place of use is the production of porcelain.
  • Microcline is used industrially in the production of glass and ceramic products.
  • It is used as ornamental lapidary material with Amazonite in green color.
  • Sometimes feldspar is also used in the manufacture of glass.

Association

Quartz, sodic plagioclase, muscovite, biotite, hornblende.

Distribution

A widespread mineral. Notable occurrences include:

  • at FredriksvÄarn, Arendal, and Larvik, Norway.
  • In the Ilmen Mountains, Ural Mountains, and on the Kola Peninsula, Russia.
  • At St. Gotthard, Ticino, Switzerland.
  • On Mt. Greiner, Zillertal, Tirol, Austria.
  • At Baveno, Piedmont, Italy.
  • In the USA, at Amelia, Amelia Co., Virginia; Haddam, Middlesex Co., Connecticut; and Magnet Cove, Hot Spring Co., Arkansas.
  • In Colorado, in the Pikes Peak area, El Paso Co., Crystal Peak, Teller Co., with large crystals from the Devil’s Hole beryl mine, Fremont Co.; in the Black Hills, Pennington and Custer Cos., South Dakota.
  • At Bancroft, Ontario, Canada.
  • From Klein Spitzkopje, Namibia.
  • In Brazil, from Minas Gerais, at Fazenda do Bananal, Salinas, Urucum, and Capelinha.
  • At Ambositra, Madagascar.
  • From Kimpusan, Yamanshi Prefecture, and Tanakamiyama, Otsu, Shiga Prefecture, Japan.
  • At Broken Hill, New South Wales, Australia.

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mindat.org. (2019). Microcline: Mineral information, data and localities.. [online] Available at: https://www.mindat.org
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