Obsidian |
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ObsidianExtrusive igneous rock of mafic composition.Rapid cooling a “dry” (water and gas-free) lava prevents crystallization, resulting in the formation of natural glass. This sample is from Obsidian Butte area located on the south shore of the Salton Sea, CA. |
| https://gotbooks.miracosta.edu/rocks/igneous/17.html | 2/2/2021 |