Obsidian

A black or dark-colored volcanic glass, usually of rhyolite composition, characterized by conchoidal fracture.
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Preliminary digital map of cryptocrystalline occurrences in northern Nevada: rkhnd (ArcView shapefile) and rkhnd_crypto (ArcInfo point coverage)

A polygon Arcview shapefile of northern Nevada cryptocrystalline occurrences derived from Nevada rockhound guides and converted to a coverage.

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