Chemical composition -- Naturally occurring volcanic glass (molten silica).
Color -- Black, gray, sometimes iridescent.
Optics-- R.I. 1.49.
Durability-- Hardness 5-6. Brittle and heat sensitive.
Crystal structure -- Amorphous.
Specific Gravity -- 2.3-3.0.
Sources -- Found in locations of volcanic activity (past or present) -- New Mexico, Hawaii, Mexico, Wyoming (Yellowstone), Utah, Japan, Iceland. Apache tears are nodules of obsidian from New Mexico, and is sometimes faceted. Snowflake obsidian, used in beads and cabochons, has whitish snowflake-like inclusions of cristobalite. Rainbow obsidian displays a colorful iridescence.