Obsidian

Obsidian is an extrusive igneous rock. It is occurring as a natural glass formed by the rapid cooling of viscous lava from volcanoes. Result of this formed, glass occupies more than 80 % and that have seeming conchoidal fracture and vitreous luster. It usually colours dark, black, grey-black to grey. Also It occur red, brown-green, green, yellow and rare transparent colourless. Colour is controlled factor by trace element content and the character of inclusion. Hand-specimen rock is common combination of two colours. Those are combination of black and brown colours.

Obsidian most frequently originates by a rapid coooling of a felsic viscous lava. Diffusion in the very viscous acid and felsic lavas with highly polymerized SiO2 tetrahedrons is slow, thus inhibiting the nucleation of crystals and supporting the origin of the glassy structure. It is fragile, tough and it disintegrates to very sharp slivers.

Name origin: The name obsidian is very old. It is ascribed to Theophrastus who used it for the first time in 320 BC. The translation into English of Natural History written by Pliny the Elder of Rome shows a few sentences on the subject of a volcanic glass called obsidian (lapis obsidianus), discovered in Ethiopia by Obsidius

Colour: Black

Structure: Massive

Texture: Glassy (vitreous, hyaline).

Alterations: Glass is neither altered nor devitrified.

Major minerals: Amorphous volcanic glass that exhibits the structural ordering similar to crystals only in very short distances. For this reason, the obsidian is sometimes regarded as a mineraloid.

Classification of Obsidian

Obsidian is a type of volcanic glass, and its classification primarily revolves around its physical characteristics, color variations, and any unique features or inclusions it may have. Here are some common classifications of obsidian:

Color Variations: Obsidian can be classified based on its color. Some common color varieties include:

Black Obsidian: This is the most common type, known for its deep black color. It’s often used for tools, jewelry, and ornamental objects.

Mahogany Obsidian: This variety has brown to reddish-brown bands or swirls, resembling the wood grain of mahogany. It’s used in jewelry and decorative items.

Rainbow Obsidian: Rainbow obsidian displays a play of colors, such as blue, green, and purple, caused by microscopic mineral crystals. It’s valued for its aesthetic appeal in jewelry and art.

Snowflake Obsidian: This type contains white or gray spherulites (small, spherical mineral clusters) that resemble snowflakes. It’s used in jewelry and ornamental objects.

Gold Sheen Obsidian: Gold sheen obsidian has a shiny, golden or metallic appearance caused by the reflection of light from microscopic gas or mineral inclusions. It’s prized for its unique luster in jewelry.

Inclusions: Obsidian can also be classified based on the types of inclusions it contains:

Pumice Obsidian: This type of obsidian may contain small fragments of pumice stone, which is another volcanic rock. The pumice fragments can create a textured appearance in the obsidian.

Magnetite or Hematite Inclusions: Some obsidian varieties contain tiny magnetite or hematite crystals, which can impart a metallic sheen or magnetic properties to the rock.

Geographical Origin: Obsidian can also be classified based on its geological source. Different regions around the world produce unique varieties of obsidian, each with its own characteristics. Examples include:

Obsidian Buttes Obsidian: From California, USA, known for its black color and use in tools.

Obsidian Cliff Obsidian: From Yellowstone National Park, USA, known for its black or banded appearance.

Armenian Obsidian: From Armenia, often characterized by its brown or gray color.

Green Obsidian: Found in various locations, including the United States and Mexico, and known for its green coloration.

Translucency: Obsidian can be classified based on its translucency. Some varieties are translucent when sliced thinly and held up to the light, allowing light to pass through.

Artistic and Cultural Classification: In the context of art or culture, obsidian objects may be classified based on their use and design. For example, obsidian knives, arrowheads, or sculptures can be classified by their intended purpose or cultural significance.

It’s important to note that the classification of obsidian can vary among geologists, mineralogists, and collectors, and there are many regional and local names for different types of obsidian based on their specific appearances and geological sources. When classifying or identifying obsidian, it’s essential to consider its color, inclusions, transparency, and geological origin to accurately describe and categorize it.

Chemical Composition of Obsidian

Obsidian is primarily composed of silicon dioxide (SiO2), which is the same chemical composition as quartz, but it has a completely different structure due to its rapid cooling from a molten state. The chemical composition of obsidian is approximately 70-75% SiO2. However, it can contain various impurities and trace elements that give rise to its different colors and varieties. These impurities can include:

1. Iron (Fe): Iron impurities can cause obsidian to appear brown or black.
2. Magnesium (Mg): Magnesium can contribute to the green coloration of some obsidian varieties.
3. Calcium (Ca): Calcium can affect the color and properties of obsidian, often resulting in shades of brown or gray.
4. Sodium (Na) and Potassium (K): These alkali metals can also be present and influence the properties of obsidian.
5. Aluminum (Al): Aluminum is another element that can be found in trace amounts in obsidian, potentially influencing its coloration.
6. Water (H2O): Some obsidian may contain small amounts of water, typically in the form of microscopic bubbles or inclusions. These water inclusions can affect the appearance and properties of obsidian.

The exact chemical composition of obsidian can vary depending on its geographical source and specific impurities present in the volcanic melt from which it formed. These impurities and trace elements are responsible for the various colors and patterns observed in different types of obsidian, such as black, brown, red, green, and translucent varieties.

Obsidian Formation

Obsidian formation is a fascinating geological process that occurs when molten lava cools rapidly, typically as a result of volcanic activity. Here’s an overview of how obsidian forms:

1. Magma Formation: The process begins deep within the Earth’s mantle, where rocks melt due to high temperatures and pressure. This molten rock is called magma.
2. Silica-Rich Composition: Obsidian is formed from magma with a particularly high silica (silicon dioxide, SiO2) content, often around 70-75%. This high silica content is a key factor in the formation of obsidian, as it influences the behavior of the molten rock.
3. Volcanic Eruption: When a volcano erupts, the magma is expelled to the Earth’s surface through volcanic vents or fissures. The rapid ascent of the magma is driven by the pressure build-up beneath the Earth’s crust.
4. Rapid Cooling: As the molten lava is exposed to the relatively cooler temperatures of the Earth’s surface, it cools rapidly. This rapid cooling prevents the formation of large mineral crystals within the lava, resulting in the formation of a glassy material instead of a crystalline one.
5. Solidification: The lava solidifies quickly into a glass-like substance known as obsidian. This process can take place within seconds to minutes, depending on the size of the lava flow and the environmental conditions.
6. Lack of Crystalline Structure: One of the defining characteristics of obsidian is its lack of a crystalline structure. Instead, it consists of a random arrangement of silica molecules, giving it its glassy and amorphous nature.
7. Conchoidal Fracture: When obsidian breaks, it exhibits conchoidal fracture, meaning it forms sharp, curved, and smooth edges. This fracture pattern is a result of the way the glassy material breaks along curved surfaces.
8. Variability: The color and appearance of obsidian can vary widely depending on factors such as impurities and mineral inclusions present in the lava. These variations give rise to different varieties of obsidian with colors ranging from black to brown, green, red, and even translucent or banded patterns.
9. Geological Setting: Obsidian is commonly found in volcanic regions around the world, typically associated with eruptions of rhyolitic or dacitic lava, which are high in silica content.

It’s worth noting that obsidian formation is just one aspect of volcanic processes, and the specific geological conditions, mineral compositions, and cooling rates can vary from one volcanic eruption to another. Obsidian is treasured for its unique appearance and sharp edges, which have made it valuable to humans for thousands of years in toolmaking, art, and cultural practices.

Occurrence

Obsidian is a naturally occurring volcanic glass that forms when molten lava cools rapidly, typically as a result of volcanic eruptions. It is known for its sharp edges and distinctive appearance, which can be shiny and black, but it can also come in other colors, including brown, gray, red, and green, depending on the impurities and mineral inclusions present.

Here are some key points about the occurrence of obsidian:

1. Volcanic Regions: Obsidian is primarily found in areas with active or dormant volcanoes. It forms when lava with a high silica content cools quickly. These volcanic regions can be found all around the world, including places like the Pacific Northwest of the United States, the Andes Mountains in South America, the Mediterranean region, Japan, and New Zealand.
2. Geological Processes: Obsidian is the result of volcanic processes. When lava is expelled from a volcano, it contains a high concentration of silica. If the lava cools quickly, either when it comes into contact with water or air, it solidifies into obsidian. The rapid cooling prevents the formation of large mineral crystals, giving obsidian its glassy texture.
3. Deposits: Obsidian can be found in various geological settings, including in lava flows, volcanic domes, and along the edges of volcanic calderas. It can also be found in layers within volcanic ash deposits.
4. Varieties: There are different varieties of obsidian, each with its own distinct characteristics. For example, snowflake obsidian contains white or gray spherulites (small, spherical mineral clusters) that resemble snowflakes, while rainbow obsidian displays a play of colors caused by microscopic mineral crystals.
5. Archaeological and Cultural Significance: Obsidian has been used by humans for thousands of years for various purposes, including tools, weapons, and ornamental objects. Archaeologists often study obsidian artifacts to trace ancient trade routes and cultural exchange.
6. Mining and Collection: Collecting obsidian requires proper permits and adherence to local regulations. It’s important to be respectful of the environment and the cultural significance of obsidian to indigenous communities when collecting or mining it.
7. Industrial Use: In addition to its historical uses, obsidian is used in modern industry for cutting tools, surgical scalpels, and in scientific applications, such as electron microscopy specimen preparation.

Keep in mind that the specific locations where you can find obsidian may vary depending on the region and geological history. If you are interested in collecting or studying obsidian in a particular area, it’s advisable to consult geological maps, local authorities, or experts to identify suitable locations and understand any legal or environmental considerations.

Properties of Obsidian

Obsidian is a unique volcanic glass known for its distinct properties. Here are some of the key properties of obsidian:

1. Color: Obsidian is typically black, but it can also come in various other colors, including brown, gray, red, green, and even translucent varieties. The specific coloration depends on impurities and mineral inclusions within the glass.
2. Luster: Obsidian has a shiny or glassy luster when polished. Its surface can be highly reflective and smooth, making it attractive for ornamental and decorative purposes.
3. Hardness: Obsidian is relatively hard, with a Mohs hardness scale rating of around 5 to 6. This makes it suitable for various applications, including making sharp cutting tools and arrowheads.
4. Conchoidal Fracture: One of the most distinctive properties of obsidian is its conchoidal fracture pattern. When it breaks, it forms sharp, curved, and smooth edges, which are ideal for creating cutting edges on tools and weapons.
5. Translucency: Some obsidian varieties can be translucent when thin slices are held up to the light. This property can make it aesthetically appealing for use in jewelry and decorative objects.
6. Density: Obsidian has a relatively high density, which means it feels heavy for its size compared to other rocks and minerals.
7. Cleavage: Unlike many minerals, obsidian does not have cleavage, meaning it does not naturally break along specific planes. Instead, it fractures in a conchoidal manner, creating sharp edges.
8. Origin: Obsidian is formed from rapidly cooled molten lava. Its glassy texture and lack of crystalline structure are due to the quick cooling process, preventing mineral crystals from forming within it.
9. Fragility: While obsidian is hard, it is also relatively brittle. It can break or chip easily upon impact, which is why it was historically used for tools and weapons with cutting edges.
10. Transparency: Some obsidian varieties, such as Apache Tears, are known for their high transparency when polished. These are often used in jewelry.
11. Inclusions: Obsidian can contain various mineral inclusions, such as cristobalite or magnetite, which can affect its appearance and properties. For example, snowflake obsidian contains white or gray spherulites that resemble snowflakes.
12. Historical and Cultural Significance: Obsidian has been used by humans for thousands of years, primarily for tools and weapons. It holds cultural and archaeological significance, as it helps trace ancient trade routes and the movement of prehistoric populations.
13. Modern Uses: In addition to its historical uses, obsidian is used in modern applications, including as a material for surgical scalpels, artistic sculptures, and gemstone beads in jewelry.

Overall, obsidian’s unique combination of properties makes it a fascinating natural material with both historical and contemporary significance. Its distinctive appearance and sharp fracture pattern make it a valuable resource for various practical and artistic purposes.

Obsidian Application and Uses Area

Obsidian has a wide range of applications and uses due to its unique properties, including its hardness, sharpness, and distinctive appearance. Here are some of the primary areas where obsidian is used:

Tools and Weapons: Historically, obsidian was a valuable material for making cutting tools, arrowheads, knives, and spear points. Its sharp edges and ability to hold a fine edge made it ideal for these purposes.

Jewelry: Obsidian’s natural beauty and the ability to be polished to a high shine make it popular in jewelry making. It is often used for beads, cabochons, pendants, and earrings. Varieties like snowflake obsidian and mahogany obsidian are particularly sought after for their unique appearances.

Art and Sculpture: Artists and sculptors use obsidian for creating intricate sculptures and decorative objects. Its smooth, reflective surface and potential for translucent varieties make it an attractive material for artistic expression.

Ornamental Objects: Obsidian is used in the production of ornamental objects such as paperweights, figurines, and collectibles. Its striking appearance adds aesthetic value to these items.

Surgical Instruments: Obsidian’s sharpness and ability to maintain a fine edge have led to its use in some surgical instruments, particularly in procedures requiring precision.

Scientific Applications: Thin sections of obsidian are used in geology and petrology for microscope slides. Researchers study these sections to learn about the volcanic processes that led to the formation of obsidian.

Metaphysical and Spiritual Practices: Some people believe that obsidian has metaphysical properties, including protective qualities and the ability to absorb negative energy. It is used in spiritual practices like crystal healing and meditation.

Lapidary and Gem Cutting: Obsidian is a popular material for lapidaries who cut and polish gemstones. Its natural glassy luster and unique patterns can make it a striking choice for gem cutting.

Archaeological Research: Obsidian artifacts, especially those with unique chemical compositions, are crucial for archaeological studies. The analysis of obsidian artifacts helps archaeologists trace ancient trade networks and understand the movements of prehistoric cultures.

Decorative Inlays: Obsidian is sometimes used as decorative inlays in furniture, sculptures, and other high-end decorative items. Its contrast with other materials can create stunning visual effects.

Museum Exhibits: Due to its historical significance and aesthetic appeal, obsidian artifacts and objects are often displayed in museums as part of archaeological and cultural exhibits.

Crafts and Hobbies: Obsidian can be used by hobbyists and craftsmen for various creative projects, such as making custom knives, creating mosaic designs, or crafting unique home decor items.

It’s important to note that while obsidian has many practical and artistic applications, its use can vary depending on its specific type and quality. Additionally, collectors and enthusiasts often value obsidian for its aesthetic qualities and the variety of colors and patterns it can exhibit. When using or working with obsidian, it’s essential to take safety precautions due to its sharp edges and brittleness.

Facts About The Rock

• Different varieties of rock get their names from their appearance.
• The appearance of it is based on the chemical composition of the magma that cooled to make the rock.
• It is also known as “nature’s glass” because of its glassy appearance.
• When It breaks, the fractures are very sharp which is why it was used as tools in the Stone Age.
• Seventy percent of obsidian rock is made of silica.
• It can only form near active volcanoes.
• Sometimes It is erupted directly from a volcano.
• The best is formed underground near a volcanic vent because those rocks will have limited impurities.
• It flows are so slow that often other obsidian flows will occur on top of each other causing a streaked appearance in the rock.
• Tiny gas bubbles that trap water are a part rock.
• Although most rocks that form in the Earth’s crust are very old, obsidian is rarely older than 20 million years old which is young for a rock.
• It goes through a process called devitrification whereby it turns from glass to a rock.
• It is commonly used during surgical procedures because it is often sharper than traditional surgical tools.
• It is used as a gemstone in jewelry.

References

• Atlas-hornin.sk. (2019). Atlas of magmatic rocks. [online] Available at: http://www.atlas-hornin.sk/en/home [Accessed 13 Mar. 2019].
• Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
• Wikipedia contributors. (2019, April 8). Obsidian. In Wikipedia, The Free Encyclopedia. Retrieved 15:17, April 10, 2019, from https://en.wikipedia.org/w/index.php?title=Obsidian&oldid=891494770
• Obsidian. (2018, December 17). New World Encyclopedia, . Retrieved 15:17, April 10, 2019 from http://www.newworldencyclopedia.org/p/index.php?title=Obsidian&oldid=1016455.
• http://www.softschools.com/facts/rocks/obsidian_rock_facts/372/