igneous

Obsidian

Obsidian (Volcanic Glass, SiO2)

Hardness: 5-5.5 Mohs; Color: Jet black to dark brown; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35-2.6

Hardness: 5-5
Color: Jet black to dark brown
Luster: Vitreous/Glassy

Identified March 28, 2026More igneous →

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Physical properties

Hardness: 5-5.5 Mohs; Color: Jet black to dark brown; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35-2.6

Formation & geological history

Formed through the rapid cooling of silica-rich (felsic) lava, which prevents the growth of crystals. Most specimens date back to the Pliocene or Pleistocene epochs (less than 65 million years old) as obsidian degrades over time due to hydration.

Uses & applications

Used in the manufacture of surgical scalpels (sharper than steel), jewelry/cabochons, ornamental carvings, and historically for arrowheads and scrapers by ancient civilizations.

Geological facts

Because it contains no crystals and breaks with sharp, curved edges, obsidian can produce a blade edge only a few nanometers thick—thinner than even the finest steel surgical tools.

Field identification & locations

Identify in the field by its smooth, glassy appearance and distinctive conchoidal fractures. Commonly found in volcanic regions such as the American Northwest (Cascades), Iceland, and Mexico. Does not have a crystalline habit.

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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