A lot of microscopic rock and mineral particles usually cause the jet black color most closely associated with obsidian. Hematite or limonite add a red or brown color to the obsidian. See the color Because pure obsidian is usually dark, on rare occasions it may also be almost white.Ĭonsider the effect of impurities on the obsidian color For examples, iron and magnesium may make obsidian dark green. Obsidian is a frozen liquid that contains small amounts of mineral impurities. It has a distinctive appearance of smooth glass. Pieces of fist size can be found on the surface in abundance here.Įxamine the obsidian’s general presence. Glass Buttes in central Oregon is one of the best places to find obsidian in the U.S. Since prehistoric times, obsidian has been used in cutting tools and is still used today in surgical scalpels.Įxplore obsidian where cooling is rapid in the margins of lava flows. How can you identify obsidian ? The lack of a crystalline structure indicates that obsidian is not a true mineral and causes extreme sharpness of the fracture surfaces. Although the newly formed obsidian has a low water content, usually less than 1 percent by weight, it is slowly hydrated to form perlite when exposed to groundwater. The existence of water speeds up this process of obsidian. Because obsidian is metastable on the surface of the Earth (the glass forms fine-grained mineral crystals over time), no obsidian older than the Cretaceous period has been found. With a similar composition, crystalline rocks include granite and rhyolite. Obsidian mainly consists of SiO2 (silicon dioxide), typically 70% or more. While obsidian is usually dark in colour, similar to basalt-like mafic rocks, the composition of obsidian is extremely felsic. It is classified as a mineraloid sometimes. Obsidian is mineral-like, but not a true mineral because it is not crystalline as a glass however, it is too complex to be categorized as a mineral.
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