Natural volcanic glass · Obsidian

Black Obsidian

Black obsidian is the plain jet-black volcanic glass: RI about 1.49, SG about 2.4, conchoidal fracture, taking a mirror polish for cabs, beads and carvings. Distinguish from black onyx and black glass by spot RI and hardness. Apache tears are its rounded pebble form.

Colour
grey

Transparency
Opaque

RI
1.480–1.510

SG
2.33–2.50

Mohs
5.0–5.5

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