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Home » Rock Tumblers » Gemstones » Obsidian

Obsidian Gemstones



What is Obsidian?



Obsidian is a glassy igneous rock that is often used as a semi-precious gemstone. It forms when molten rhyolitic rock material cools so quickly that crystalline mineral structures are not produced. This can occur when the molten rock makes contact with water or is thrown through the air.

Most obsidian specimens are black in color with a bright vitreous luster. Brown obsidians are very popular and are known as “mahogany obsidian” in the gemstone trade. Greenish obsidians are also common. A small number of obsidian specimens have a gold, silver or peacock-color sheen or iridescence caused by inclusions of air or tiny mineral grains. These interesting lusters make the stones popular. Other obsidians contain white, radial inclusions of cristobalite. When polished they have a snowflake appearance giving these stones the name “snowflake obsidian”.


Obsidian Gemstones:



Obsidian is often sold as a gemstone and used in jewelry. Tumble-polished obsidian is used to make inexpensive jewelry. Obsidian is also cut en cabochon or into beads for use in pendants, earrings, necklaces, rings and cuff links. With a hardness of 5 to 5.5 obsidian is soft for certain gemstone uses. It is very well suited for pendants and earrings. However, because obsidian scratches and breaks easily it is not a good gemstone in jewelry that might be subject to impact or abrasion.


Tumbled Obsidian:



Obsidian is often used as a tumbling rough and the vitreous black tumbled stones are very attractive. It is best tumbled by people who have experience because it is a brittle stone. Tumbling with plastic pellets or other cushioning materials will help prevent breaks, chips and bruises. Obsidian is also soft, with a hardness of 5 to 5.5. It is best tumbled with materials of similar hardness. It will wear away quickly if tumbled with quartz, agate or jasper.

Rough obsidian with mahogany swrils
Rough black obsidian with mahogany swirls. Image © iStockphoto / Sean Curry.

More About Obsidian:



Because obsidian does not have a uniform crystalline structure it breaks with a conchoidal fracture. This breakage produces very sharp edges. Early people took advantage of this and chipped obsidian into sharp objects such as knives and projectile points. Today it is still used to make cutting tools such as ultra sharp blades for microsurgery.


Rough snowflake obsidian
Snowflake obsidian rough. Image © iStockphoto / Fernando Sanchez.
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Rainbow Obsidian
Tumble polished rainbow obsidian. Image © geology.com.


Mahogany obsidian gemstone
Tumble polished mahogany obsidian. Image © iStockphoto / Arpad Benedek.

Snowflake obsidian tumbled gemstone
Tumble polished snowflake obsidian. Image © iStockphoto / Alexandar Iotzov

 Tumbled Gemstone Gallery
Agate
Amazonite
Apatite
Aventurine
Carnelian
Chalcedony
Chrysoprase
Jasper
Kyanite
Labradorite
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Mookaite
Obsidian
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Sodalite
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