igneous

Black Obsidian

Obsidian (Volcanic Glass)

Hardness: 5-5.5 (Mohs scale); Color: Jet black, sometimes slightly translucent at edges; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35-2.60.

Hardness: 5-5
Color: Jet black, sometimes slightly translucent at edges
Luster: Vitreous (glassy)

Identified June 3, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of silica-rich (felsic) lava, which prevents crystal growth. It is typically associated with rhyolitic volcanic activity from the Cenozoic era to recent times.

Uses & applications

Used in ornamental jewelry, decorative items, and historically for sharp tools like arrowheads and sacrificial knives. Today, it is occasionally used in surgical scalpel blades for its extreme sharpness.

Geological facts

Because it has no crystal structure, its edges can be thinned down to almost molecular thickness, making it sharper than high-quality steel scalpels. Famous varieties include Snowflake, Mahogany, and Rainbow Obsidian.

Field identification & locations

Identify in the field by its distinct glassy luster and smooth, curved conchoidal fractures. Commonly found in volcanic regions such as the American Northwest, Mexico, Iceland, and Italy. Collectors look for unique inclusions or color sheen.

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