Igneous

Obsidian

Volcanic Glass (comprised primarily of SiO2)

Hardness: 5-5.5 on Mohs scale; Color: typically jet black but can be grey or green; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35-2.6

Hardness: 5-5
Color: typically jet black but can be grey or green
Luster: Vitreous/Glassy

Identified March 14, 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. Most specimens belong to the Cenozoic era, as volcanic glass eventually devitrifies into crystal over millions of years.

Uses & applications

Historically used for arrowheads and blades; currently used in high-end surgical scalpels, jewelry (cabochons), and ornamental carvings.

Geological facts

Because it has no crystal structure, obsidian can be fractured to an edge only a few molecules thick, making it significantly sharper than high-quality steel scalpels. It is technically a mineraloid, not a true mineral, because it lacks a crystal lattice.

Field identification & locations

Identify in the field by its distinct glassy texture, sharp edges, and unique radial 'conchoidal' fracture lines. Common in volcanic regions such as the American West (Oregon, California), Iceland, and Mexico.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral