igneous

Obsidian

Volcanic Glass (70% or more SiO2)

Hardness: 5-6 (Mohs); Color: Jet black to dark grey/green; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.4

Hardness: 5-6 (Mohs)
Color: Jet black to dark grey/green
Luster: Vitreous/Glassy

Identified February 12, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs); Color: Jet black to dark grey/green; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.4

Formation & geological history

Formed through the extremely rapid cooling of felsic (silica-rich) lava, preventing crystal growth. Usually found in volcanic regions of any geological age where high-silica eruptions occurred.

Uses & applications

Historically used for cutting tools, arrowheads, and mirrors. Modern uses include surgical scalpel blades, jewelry (cabochons), and ornamental home decor.

Geological facts

Because it is glass, obsidian is chemically unstable over long geological time and eventually 'devitrifies' into quartz crystals. It has one of the sharpest edges known to man, far finer than a steel blade.

Field identification & locations

Identify by its distinct conchoidal fracture and sharp, glass-like edges. Commonly found in Oregon, Mexico, Iceland, and Italy. Collectors look for unique patterns like 'Snowflake' or 'Rainbow' sheen.

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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