igneous

Obsidian

Volcanic Glass (Extrusive Igneous Rock, primarily SiO2)

Hardness: 5–6 Mohs; Color: Typically black, but can be mahogany, sheen, or snowflake; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (has conchoidal fracture); Specific Gravity: 2.35–2.6.

Hardness: 5–6 Mohs
Color: Typically black, but can be mahogany, sheen, or snowflake
Luster: Vitreous/Glassy

Identified March 7, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of felsic (silica-rich) lava, which prevents crystal growth. It is geologically young because it eventually devitrifies into crystalline material. Found in volcanic regions worldwide.

Uses & applications

Used historically for sharp tools and weapons (arrowheads, knives). Currently used for surgical scalpel blades, jewelry (cabochons), ornamental decor, and as a semi-precious gemstone.

Geological facts

Ancient civilizations used it for mirrors and blades. Because it breaks with a conchoidal fracture, the edges can be thinner and sharper than high-quality steel, even down to a single molecular layer.

Field identification & locations

Identify in the field by its distinct glassy appearance and characteristic curved, shell-like (conchoidal) fractures. Found in volcanic fields like Glass Buttes, Oregon, or the Yellowstone area. Collectors look for unique patterns like 'Snowflake' or 'Mahogany'.

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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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral