igneous

Obsidian

Obsidian (Volcanic Glass)

Hardness: 5–5.5 Mohs scale; Color: Black to dark brown/grey (translucent at edges); Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6.

Hardness: 5–5
Color: Black to dark brown/grey (translucent at edges)
Luster: Vitreous/Glassy

Identified April 5, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of silica-rich (felsic) lava, which prevents crystal growth. Usually found in geologically recent volcanic fields or areas with high rhyolitic volcanic activity.

Uses & applications

Used historically for sharp tools and weapons (scalpels, arrowheads). Modern uses include ornamental carvings, jewelry, and high-quality surgical blades.

Geological facts

Obsidian was so highly valued by ancient civilizations that it was traded over thousands of miles. It can produce a cutting edge many times sharper than premium steel surgical scalpels.

Field identification & locations

Identify in the field by its characteristic smooth, curved (conchoidal) glass-like fracture and extremely sharp edges. Commonly found in Oregon (USA), Mexico, and Iceland.

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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