Obsidian

Physical Properties

Hardness: 5-6 (Mohs); Color: Jet black to dark brown; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.3-2.5

Formation & Geological History

Formed through the rapid cooling of silica-rich (felsic) lava, preventing crystal growth. Usually found in volcanic regions from the Cenozoic era or younger, as glass eventually devitrifies into crystals over millions of years.

Uses & Applications

Used in surgical scalpels for precision, jewelry (beads/cabochons), flintknapping for primitive weapons/tools, and popular as a decorative metaphysical stone.

Geological Facts

Because it breaks with a conchoidal fracture, obsidian can be honed to an edge one molecule thick—five hundred times sharper than the sharpest steel blade. Native Americans used it extensively for arrowheads and trade.

Field Identification & Locations

Identify in the field by its distinctive glassy appearance and sharp, curved edges. Commonly found in areas of recent volcanic activity like the American West (Glass Buttes, Oregon or Obsidian Cliff, Yellowstone).

Identified on: 4/19/2026

Mode: Standard