igneous

Obsidian

Volcanic Glass (SiO2)

Hardness: 5-6 (Mohs scale); Color: Typically black or dark brown; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6

Hardness: 5-6 (Mohs scale)
Color: Typically black or dark brown
Luster: Vitreous (glassy)

Identified March 23, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of silica-rich (felsic) lava. The cooling occurs so quickly that atoms are unable to arrange themselves into a crystalline structure. Found in geologically young volcanic regions worldwide.

Uses & applications

Historically used for arrowheads and blades; currently used in scalpels for heart and eye surgery, decorative jewelry (cabochons), and as a collector's item.

Geological facts

Because it is not a mineral (having no crystal structure), it is technically a 'mineraloid.' It breaks with a conchoidal fracture, creating edges that can be sharper than high-quality surgical steel.

Field identification & locations

Identify by its intense glassy luster and curved, shell-like (conchoidal) fracture lines. Commonly found in Oregon, California, and Iceland. Collectors should look for unique inclusions like 'snowflake' patterns or 'rainbow' sheen.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous