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Natural Black Obsidian Rough Stone (3 pieces lot)
Weight per piece: 14, 14.5, 18 gram (total 46.5 g)
Sizes: 28x22x16, 28x24x17, 29x27x18 mm
These stones are from Africa.
***
Obsidian
Category Volcanic glass
Chemical formula 70–75% SiO2, plus MgO, Fe3O4
Color Black
Fracture Conchoidal
Mohs scale hardness 5–6
Luster Vitreous
Specific gravity ~2.4
Optical properties Translucent
Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock.
It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth. Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition (high silica content) induces a high viscosity and polymerization degree of the lava. The inhibition of atomic diffusion through this highly viscous and polymerized lava explains the lack of crystal growth. Obsidian is hard and brittle; it therefore fractures with very sharp edges, which had been used in the past in cutting and piercing tools, and are still used as surgical scalpel blades.
Obsidian is the rock formed as a result of cooled magma, which is the parent material. Having a low water content when newly formed typically less than 1% water by weight, becomes progressively hydrated when exposed to groundwater, forming perlite. Tektites were once thought by many to be obsidian produced by lunar volcanic eruptions, though few scientists now adhere to this hypothesis.
Obsidian is mineral-like, but not a true mineral because as a glass it is not crystalline; in addition, its composition is too complex to comprise a single mineral. It is sometimes classified as a mineraloid. Though obsidian is usually dark in color similar to mafic rocks such as basalt, obsidian's composition is extremely felsic. Obsidian consists mainly of SiO2 (silicon dioxide), usually 70% or more. Crystalline rocks with obsidian's composition include granite and rhyolite. Because obsidian is metastable at the Earth's surface (over time the glass becomes fine-grained mineral crystals), no obsidian has been found that is older than Cretaceous age. This breakdown of obsidian is accelerated by the presence of water.
Pure obsidian is usually dark in appearance, though the color varies depending on the presence of impurities. Iron and magnesium typically give the obsidian a dark brown to black color. Very few samples are nearly colorless. In some stones, the inclusion of small, white, radially clustered crystals of cristobalite in the black glass produce a blotchy or snowflake pattern (snowflake obsidian). It may contain patterns of gas bubbles remaining from the lava flow, aligned along layers created as the molten rock was flowing before being cooled. These bubbles can produce interesting effects such as a golden sheen (sheen obsidian) or an iridescent, rainbow-like sheen (rainbow obsidian).
Obsidian can be found in locations which have experienced rhyolitic eruptions.
Item Specifics | |
---|---|
Gemstone Shape : | Rough |
Certification : | N/A |
Wholesale : | No |
Gemstone Creation : | Natural |
Item Width : | N/A |
Gemstone Color : | Black |
Number of Pieces : | 3 |
Modified Item : | No |
Item Length : | N/A |
Vintage : | No |
Cut Grade : | Good |
Gemstone Clarity Grade : | Eye Clean |
Country/Region of Manufacture : | China |
Transparency : | Opaque |
Gemstone Type : | Obsidian |
Gemstone Form : | Rough |
Shape : | Rough |
Treatment : | Not Enhanced |
Natural/Lab-Created : | Natural |
Gemstone Effect : | Iridescence |
Gemstone Treatment : | Not Enhanced |
Total Carat Weight (TCW) : | 232.5 |
Brand : | Unbranded |
Country of Origin : | China |
Color : | Black |
Item Depth : | N/A |
Carat Range : | Greater than 6.00 |
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We send the goods to USA, Canada, UK, Australia, New Zealand, EU countries and some other European and Asian countries by E-express, a kind of fast postal service by Hong Kong Post. It usually takes about 6 to 10 working days for delivery.
We send the goods to other countries by registered airmail and will take about 8 to 14 working days for delivery.
Returns: We accept returns with any reason in 30 days.
We will answer buyer messages within 24 hours during working days.
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Black Obsidian Rough Stone 3 pieces Lot 46.5 gram
Natural Black Obsidian Rough Stone (3 pieces lot)
Weight per piece: 14, 14.5, 18 gram (total 46.5 g)
Sizes: 28x22x16, 28x24x17, 29x27x18 mm
These stones are from Africa.
*** Obsidian Category Volcanic glass Chemical formula 70–75% SiO2, plus MgO, Fe3O4 Color Black Fracture Conchoidal Mohs scale hardness 5–6 Luster Vitreous Specific gravity ~2.4 Optical properties Translucent Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth. Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition (high silica content) induces a high viscosity and polymerization degree of the lava. The inhibition of atomic diffusion through this highly viscous and polymerized lava explains the lack of crystal growth. Obsidian is hard and brittle; it therefore fractures with very sharp edges, which had been used in the past in cutting and piercing tools, and are still used as surgical scalpel blades. Obsidian is the rock formed as a result of cooled magma, which is the parent material. Having a low water content when newly formed typically less than 1% water by weight, becomes progressively hydrated when exposed to groundwater, forming perlite. Tektites were once thought by many to be obsidian produced by lunar volcanic eruptions, though few scientists now adhere to this hypothesis. Obsidian is mineral-like, but not a true mineral because as a glass it is not crystalline; in addition, its composition is too complex to comprise a single mineral. It is sometimes classified as a mineraloid. Though obsidian is usually dark in color similar to mafic rocks such as basalt, obsidian's composition is extremely felsic. Obsidian consists mainly of SiO2 (silicon dioxide), usually 70% or more. Crystalline rocks with obsidian's composition include granite and rhyolite. Because obsidian is metastable at the Earth's surface (over time the glass becomes fine-grained mineral crystals), no obsidian has been found that is older than Cretaceous age. This breakdown of obsidian is accelerated by the presence of water. Pure obsidian is usually dark in appearance, though the color varies depending on the presence of impurities. Iron and magnesium typically give the obsidian a dark brown to black color. Very few samples are nearly colorless. In some stones, the inclusion of small, white, radially clustered crystals of cristobalite in the black glass produce a blotchy or snowflake pattern (snowflake obsidian). It may contain patterns of gas bubbles remaining from the lava flow, aligned along layers created as the molten rock was flowing before being cooled. These bubbles can produce interesting effects such as a golden sheen (sheen obsidian) or an iridescent, rainbow-like sheen (rainbow obsidian). Obsidian can be found in locations which have experienced rhyolitic eruptions.
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By Paypal Shipping
Free shipping cost. We send the goods to USA, Canada, UK, Australia, New Zealand, EU countries and some other European and Asian countries by E-express, a kind of fast postal service by Hong Kong Post. It usually takes about 6 to 10 working days for delivery. We send the goods to other countries by registered airmail and will take about 8 to 14 working days for delivery. Returns
Returns: We accept returns with any reason in 30 days. Contact Us
We will answer buyer messages within 24 hours during working days. All right reserved. |
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