obsidian

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Photo courtesy of Scott Papper, GIA GG, AJP, Global Gemology & Appraisals

Species:  Obsidian
Mohs Hardness:  5 to 6 out of 10
Color:  Dark green or brown to black
RI:  1.490 (+0.020/-0.010)
Birefringence:  None
SR/DR/AGG:  SR, commonly with ADR
Spectrum:  Not diagnostic
Fluorescence:  Generally inert
SG:  2.40 (+0.10/-0.07)

obsidian facts

Photo courtesy of Scott Papper, GIA GG, AJP, Global Gemology & Appraisals

Obsidian is a natural glass formed by the rapid cooling of volcanic lava.

Obsidian is hard yet brittle, chipping easily, leaving sharp edges.  In ancient times, obsidian was sharpened into blades and arrowheads.

Sheen obsidian has either a golden or silver aventurescent sheen.
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