Apatite is a group of phosphate minerals commonly found in a variety of geological environments. It is an important mineral due to its role in the formation of bones and teeth in living organisms, and is also used as a source of phosphorus for fertilizers. Apatite typically forms in a range of colors, including green, yellow, blue, and colorless. It can be transparent to opaque, and its crystals often have a hexagonal or prismatic shape.

Historical Significance and Discovery: The name “apatite” is derived from the Greek word “apatao,” which means “to deceive,” because of its resemblance to other minerals, such as peridot and beryl, which often led to confusion among early mineralogists. Apatite has been known since antiquity, but it wasn’t until the 19th century that scientists were able to clearly identify and distinguish it from other minerals.

Chemical Formula (Ca5(PO4)3(F,Cl,OH)): The chemical formula for apatite can vary slightly depending on the presence of different elements. The most common form of apatite is calcium phosphate, with the general formula:

  • Ca₅(PO₄)₃(F,Cl,OH)

This formula reflects the presence of calcium (Ca), phosphate groups (PO₄), and different halide ions such as fluoride (F), chloride (Cl), or hydroxide (OH). These variations give rise to different types of apatite minerals, including fluorapatite, chlorapatite, and hydroxyapatite, each differing in their halide composition.

Types of Apatite

Apatite is a group of phosphate minerals that can be classified based on the halide component present in their structure. The main types of apatite are:

  1. Fluorapatite (Ca₅(PO₄)₃F)
    • Chemical Composition: Calcium phosphate with fluoride (F) as the halide.
    • Characteristics: Fluorapatite is the most common form of apatite found in nature. It is highly resistant to weathering and is a major component of bones and teeth in humans and animals. This type is also widely used in the production of fertilizers.
    • Occurrence: Found in igneous rocks, as well as in sedimentary and metamorphic environments.
    • Significance: It is an important source of fluoride and phosphorus.
  2. Chlorapatite (Ca₅(PO₄)₃Cl)
    • Chemical Composition: Calcium phosphate with chloride (Cl) as the halide.
    • Characteristics: Chlorapatite is rarer than fluorapatite. Its properties are similar to fluorapatite, but it is less resistant to weathering. The chloride ion in the structure gives it distinct characteristics compared to the fluoride form.
    • Occurrence: It can be found in certain metamorphic rocks and in igneous deposits.
    • Significance: Less common but important in geological studies and certain mineralogical contexts.
  3. Hydroxyapatite (Ca₅(PO₄)₃OH)
    • Chemical Composition: Calcium phosphate with hydroxide (OH) as the halide.
    • Characteristics: Hydroxyapatite is the primary mineral found in human and animal bones and teeth. It is naturally occurring and is the most stable form of apatite under normal conditions.
    • Occurrence: Common in biological systems and is found in the bones and teeth of vertebrates. It also occurs in certain sedimentary rocks and as a product of geological processes.
    • Significance: Hydroxyapatite is used in medical and dental applications, particularly for bone grafts and dental implants.
  4. Manganese Apatite (Ca₅(PO₄)₃(Mn))
    • Chemical Composition: Similar to other apatites but with manganese (Mn) replacing calcium in the structure.
    • Characteristics: This type is often colored due to the presence of manganese and can appear in shades of purple, pink, or red.
    • Occurrence: Found in metamorphic rocks and some igneous deposits, particularly in areas with high manganese content.
  5. Carbonate Apatite (Ca₅(PO₄)₃(CO₃))
    • Chemical Composition: Calcium phosphate with carbonate (CO₃) ions in place of some of the phosphate groups.
    • Characteristics: This type of apatite occurs with carbonate substitutions, which can affect its crystal structure and properties. It may appear in white or cream-colored forms.
    • Occurrence: Common in sedimentary rocks and biogenic materials, including fossils and some bone material.

Each of these types of apatite can have distinct properties, uses, and occurrences in nature, making them significant both geologically and biologically.

Physical Properties of Apatite

Apatite is a group of minerals with varying physical properties depending on its type (fluorapatite, chlorapatite, hydroxyapatite, etc.), but there are several key physical characteristics that are commonly observed in most apatite specimens:

  1. Color:
    • Apatite can occur in a wide range of colors, including green, yellow, blue, colorless, brown, purple, and even pink. The color depends on the specific type of apatite and the presence of trace elements or impurities.
    • Commonly seen colors: Green (most common), yellow, and bluish hues.
  2. Transparency:
    • Apatite can be transparent, translucent, or opaque. Transparent specimens are often used in gemstones, while opaque forms are more commonly found in natural mineral deposits.
  3. Luster:
    • The luster of apatite is typically vitreous (glass-like) or greasy when it is not well-formed. The surface can sometimes appear dull depending on its crystal quality and exposure to the environment.
  4. Hardness:
    • Apatite has a Mohs hardness of 5, which means it is relatively soft compared to other minerals like quartz (7) but harder than many other common minerals like gypsum (2) or calcite (3).
    • This hardness makes apatite easy to scratch with harder minerals but still durable for use in certain applications, such as gemstones or fertilizers.
  5. Cleavage:
    • Apatite exhibits imperfect cleavage in one direction. This means that it can break along certain planes, but the cleavage is not as perfect as minerals like mica or feldspar. The cleavage can result in uneven, rough fractures, which can affect the appearance of apatite crystals.
  6. Fracture:
    • When apatite fractures, it typically breaks with a conchoidal (shell-like) fracture, especially if it is a harder or more well-formed crystal. Fracture surfaces can be smooth or uneven depending on the type of break.
  7. Density:
    • Apatite has a relatively low to moderate density, typically ranging between 3.1 and 3.2 g/cm³. This density varies slightly depending on the presence of different halides or impurities in the structure.
  8. Crystal System:
    • Apatite crystals belong to the hexagonal crystal system, meaning that they often form prismatic crystals, which can appear as slender rods or prisms, typically with hexagonal cross-sections. The crystals are usually elongated and can form aggregates, such as clusters or masses.
  9. Specific Gravity:
    • The specific gravity of apatite generally ranges from 3.1 to 3.2. This indicates how much denser apatite is compared to water.
  10. Magnetism:
    • Apatite is non-magnetic, meaning it does not exhibit magnetic properties under normal conditions. However, specific apatite samples with certain impurities may show slight magnetic behavior.
  11. Refractive Index:
    • Apatite has a refractive index of about 1.63 to 1.64, which is relatively low but noticeable when used in gemstones and cut as faceted stones.

Geological Occurrence of Apatite

Apatite is a widely distributed mineral and can be found in a variety of geological environments. It forms under a range of conditions, from igneous to sedimentary and metamorphic settings. Here’s an overview of where and how apatite occurs:

  1. Igneous Rocks:
    • Apatite is commonly found in igneous rocks, particularly in granites, basalts, and syenites. In these rocks, apatite typically forms as a primary accessory mineral, often crystallizing from the cooling magma.
    • Apatite forms as small crystals within the rock matrix, typically as prismatic or needle-like structures.
    • Granite and gabbro are examples of igneous rocks that often contain apatite. These rocks, particularly those with high phosphorus content, can host significant amounts of apatite.
  2. Metamorphic Rocks:
    • Apatite can also be found in metamorphic rocks, where it forms during the recrystallization of minerals under high pressure and temperature conditions.
    • In marbles, schists, and gneisses, apatite often occurs as a result of the metamorphism of phosphorus-rich rocks, like phosphate-bearing limestones.
    • It can also form as a secondary mineral during the alteration of primary phosphate deposits, especially in regions undergoing high-grade metamorphism.
  3. Sedimentary Rocks:
    • Apatite is present in some sedimentary rocks and is often found in phosphorite or rock phosphate deposits. These deposits form when phosphorus-rich materials, such as organic matter or bones, are concentrated over time through the processes of erosion and sedimentation.
    • Apatite-rich sediments are typically deposited in shallow marine environments where organic material accumulates and undergoes chemical alteration.
    • Phosphorite beds are important sources of phosphate, and the apatite found in these beds is often rich in fluorapatite or hydroxyapatite.
    • Phosphorite deposits are mined for their high phosphorus content, which is used to produce fertilizers.
  4. Biological Deposits:
    • Apatite also forms in biological systems. It is a major component of the bones and teeth of vertebrates, making it an important mineral for understanding the geology of life and the fossil record.
    • In marine organisms, apatite occurs as part of the calcareous shells of some marine life, particularly in fish bones and marine invertebrates.
  5. Hydrothermal Environments:
    • Apatite can also form in hydrothermal veins and hot spring deposits. These deposits occur when hot, mineral-rich fluids interact with surrounding rocks, leading to the precipitation of apatite along with other minerals such as calcite, quartz, or barite.
    • Apatite can be part of the mineralization in hydrothermal ore deposits, particularly where phosphorus-bearing fluids are present.
  6. Meteorites:
    • In rare cases, apatite has been found in meteorites, specifically in carbonaceous chondrites. These extraterrestrial rocks contain apatite as part of their mineral content, providing clues about the early solar system and the processes involved in the formation of planets and other celestial bodies.

Global Distribution of Apatite

  • Canada, Russia, and Morocco are among the world’s leading producers of phosphate rock, which contains significant amounts of apatite.
  • Florida (USA) and China are also significant sources of apatite in the form of phosphorite deposits.
  • India and Brazil have large phosphate mining operations, further contributing to global apatite availability.

Economic Importance

Apatite’s occurrence in phosphate deposits makes it a vital mineral in the global economy, particularly for the production of fertilizers. The phosphorus extracted from apatite is a key ingredient in fertilizers that are essential for agriculture. Phosphate deposits are often mined directly for their apatite content, which is processed to extract phosphorus for agricultural use.

Apatite is also important in geochronology, where the uranium and thorium isotopes present in some apatite minerals are used for dating rocks and minerals.

Uses of Apatite

Apatite is a versatile mineral with a range of uses, both in industry and in biological contexts. Its primary applications are related to its phosphorus content, but it also has significance in other fields, including geology and technology.

1. Fertilizers:

  • Primary Use: The most significant use of apatite is in the production of phosphate fertilizers. Apatite is a major source of phosphorus, an essential nutrient for plant growth.
  • Phosphorite Mining: Apatite-rich phosphorite deposits are mined and processed to produce phosphoric acid, which is then used to create various forms of phosphate fertilizers, such as superphosphate and triple superphosphate.
  • Global Demand: As phosphorus is a critical nutrient for crop production, apatite-based fertilizers are crucial for global agriculture. The demand for phosphate fertilizers drives much of the mining and processing of apatite worldwide.

2. Animal Feed:

  • Phosphorus is also an essential component of animal nutrition. Apatite is sometimes processed and included in animal feed to supply phosphorus, which is necessary for bone growth, energy transfer, and overall health.
  • This use is especially significant in regions where there are phosphate deficiencies in local feedstocks.

3. Production of Phosphoric Acid:

  • Industrial Application: Apatite is used to produce phosphoric acid through a process called wet-process phosphoric acid production. Phosphoric acid is a key ingredient in various industrial processes, such as the production of detergents, food additives, and in the treatment of water.
  • Phosphoric acid is also used to produce high-grade phosphorus chemicals, such as phosphates used in detergents, flame retardants, and water treatment chemicals.

4. Manufacture of Phosphorus Compounds:

  • Apatite is a key raw material for the production of a range of phosphorus compounds, including:
    • Calcium phosphate (used in ceramics, dental products, and food supplements).
    • Phosphoric acid (used in fertilizers, food processing, and cleaning agents).
    • Tricalcium phosphate (used in food supplements and as a food additive).
    • Phosphate salts (used in many industrial and household applications).

5. Gemstones and Jewelry:

  • Apatite as a Gemstone: While not as common as other gemstones, apatite is sometimes cut and polished for use in gemstones. Transparent or lightly colored specimens are valued for their glassy luster and vibrant colors, particularly in shades of blue and green.
  • Jewelry Use: When cut into faceted stones, apatite can be used in rings, earrings, and pendants. However, due to its relatively low hardness (5 on the Mohs scale), it is not as durable as other gemstones like sapphire or diamond.

6. Biological Applications:

  • Bone and Dental Materials:
    • Hydroxyapatite (a form of apatite) is a key component of bone and teeth in humans and animals. This mineral’s structure closely resembles the inorganic portion of bone and enamel, making it crucial in biological systems.
    • Synthetic hydroxyapatite is used in medical applications, such as in the production of bone grafts, dental implants, and other prosthetic devices. Its biocompatibility allows it to bond well with natural bone, facilitating healing and integration.
  • Bone Tissue Engineering: Hydroxyapatite is also widely used in bone tissue engineering as a scaffold material for growing new bone tissues. Its use in regenerative medicine helps in repairing or replacing damaged bones.

7. Geological and Gemological Research:

  • Geochronology: Apatite is useful in geochronology for dating rocks and minerals. Apatite crystals can contain trace amounts of uranium and thorium, which decay over time, allowing scientists to estimate the age of the rock in which they are found through the measurement of fission tracks or (U-Th)/He dating methods.
  • Gemological Studies: Apatite is studied in gemology for its properties as a gemstone, helping to determine its value and characteristics in comparison to other minerals.

8. Manufacture of Ceramic Products:

  • Calcium phosphate derived from apatite is used in the production of ceramic materials, particularly in the creation of porcelain and high-performance ceramics. These ceramics may be used in various industrial applications, including coatings, electronics, and insulation materials.

9. Water Treatment:

  • Phosphate-based Compounds: Apatite’s derivatives are sometimes used in water treatment. For example, phosphate compounds are added to municipal and industrial water systems to prevent corrosion and scale buildup in pipes and machinery.

10. Other Miscellaneous Uses:

  • Pigments and Paints: Some forms of apatite, particularly phosphate salts, are used in the production of pigments and paints. The colorants can be used in a variety of industrial and artistic applications.
  • Fluoride Source: Fluorapatite, which contains fluoride, can also be a source of fluoride for fluoride-based compounds used in toothpaste and water fluoridation.

Apatite is an essential mineral with a wide range of uses, from its primary role in the production of fertilizers to its applications in medicine, industry, and even jewelry. Its versatility and critical role in biological and industrial processes make it one of the most important minerals in the world today.

Phosphate Rock

Phosphate rock and phosphorite are names used for sedimentary rocks that contain at least 15% to 20% phosphate on the basis of weight. The phosphorous content in these rocks is mainly derived from the presence of apatite minerals

Uses of Apatite as Phosphate Rock

  • Most of the phosphate rock mined throughout the world is used to produce phosphate fertilizer. It is also used to produce animal feed supplements, phosphoric acid, elemental phosphorous, and phosphate compounds for the chemical industry.
  • China is the largest producer of phosphate rock, producing approximately 100 million tons in 2014. The United States, Russia, Morocco, and Western Sahara are also major phosphate producers.
  • Over 75% of the world’s reserves of phosphate rock are located in Morocco and Western Sahara.

Apatite FAQ

What is apatite used for?

Apatite is used in various fields, including agriculture, industry, medicine, and research. It is a major source of phosphate, which is used in fertilizers, and it is also used in the production of phosphoric acid, ceramics, dental implants, and jewelry.

What are the physical properties of apatite?

Apatite is typically green, brown, blue, or yellow, and it has a hardness of 5 on the Mohs scale. It has a specific gravity of around 3.2 to 3.4, and it typically has a hexagonal crystal structure.

Where is apatite found?

Apatite is found in many locations around the world, including Canada, Brazil, Russia, and Madagascar. It can occur in a variety of geological environments, such as igneous rocks, sedimentary rocks, and hydrothermal veins.

Is apatite radioactive?

Some apatite can be radioactive, particularly if it contains trace amounts of uranium or other radioactive elements. However, not all apatite is radioactive, and its radioactivity can vary depending on the specific location and composition of the mineral.

What is the chemical composition of apatite?

Apatite has a complex chemical composition that can vary depending on the specific type of apatite. The basic formula for apatite is Ca5(PO4)3X, where X can be any one of several ions, including OH-, F-, Cl-, or a combination of these. Apatite can also contain various trace elements and impurities, which can affect its properties and behavior.

References

  • Hobart M. King (2018) Apatite, Phosphorite and Phosphate Rock https://geology.com/minerals/apatite.shtml
  • Market Price , https://roughmarket.com/apatite/
  • Arem,J,E.,Smigel,B (2018) Apatite Value, Price, and Jewelry Information, International Gem Society
  • Villalba,G.,Ayres, R,U.,Schroder, H(2008). “Accounting for Fluorine: Production, Use, and Loss”. Journal of Industrial Ecology.
  • USGS, Mineral commodity summaries, Available at http://minerals. usgs.gov/minerals/pubs/commodity/phosphate_rock/index.html#mcs verified 19 April 2013).

RELATED ARTICLESMORE FROM AUTHOR