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) Routine Treatments: None
Photo courtesy of Scott Papper, GIA GG, AJP, CM (NAJA), 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.