Obsidian

Physical Properties

Hardness: 5-5.5 Mohs; Color: Typically black but can be brown or green; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None, exhibits conchoidal fracture; Specific Gravity: 2.4

Formation & Geological History

Formed through the extremely rapid cooling of felsic (silica-rich) lava, which prevents crystal growth. It is primarily associated with geologically recent volcanic activity due to its unstable nature over long periods of time.

Uses & Applications

Used historically for sharp tools and weapons (arrowheads, sacrificial knives). Modern uses include high-end surgical scalpel blades, jewelry, decorative carvings, and metaphysical collecting.

Geological Facts

Obsidian is technically a supercooled liquid because it lacks a crystal structure. Over time, it 'devitrifies' or breaks down, turning into crystalline minerals like quartz; thus, few obsidian specimens are older than a few million years.

Field Identification & Locations

Identify in the field by its distinct glass-like sheen and sharp, curved (conchoidal) edges when broken. It is commonly found in volcanic regions such as the American Northwest, Iceland, Mexico, and Japan.

Identified on: 4/14/2026

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