obsidian
Instance URI: http://resource.geosciml.org/classifier/cgi/commodity-code/obsidian
Within scheme: South Australian Commodity Codes
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.