Obsidian

Physical Properties

Hardness: 5–6 (Mohs scale); Color: Jet black; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6

Formation & Geological History

Formed through the rapid cooling of felsic (silica-rich) lava, which prevents the growth of crystals. It is typically found in geologically young areas such as the Pliocene to Holocene epochs due to its tendency to devitrify over time.

Uses & Applications

Used historically for sharp tools and weapons (arrowheads, knives); currently used in jewelry (beads, cabochons), high-end surgical scalpels, and as decorative ornamental pieces.

Geological Facts

Obsidian is technically a glass rather than a true mineral because it lacks a crystalline structure. Ancient civilizations used it for mirrors and it was a highly traded commodity in Mesoamerica.

Field Identification & Locations

Identify in the field by its distinct jet-black color, sharp edges, and smooth, curved (conchoidal) fracture surfaces that resemble broken glass. Commonly found in volcanic regions like the American Northwest, Iceland, and Mexico.

Identified on: 4/23/2026

Mode: Standard