http://resource.geosciml.org/classifier/cgi/commodity-code/obsidian
definition | Obsidian is the result of volcanic lava coming in contact with water. Often the lava pours into a lake or ocean and is cooled quickly. This process produces a glassy texture in the resulting rock. Iron and magnesium give the obsidian a dark green to black color. Obsidian has been used by ancient people as a cutting tool, for weapons, and for ceremonial purposes and is sometimes found by archaeologists in excavations. | ![]() |
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source | http://www.galleries.com/Obsidian | ![]() |
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is primary topic of | obsidian |