igneous

Obsidian (worked into an arrowhead profile)

Obsidian (volcanic glass), primarily SiO2 (Silicon Dioxide)

Hardness: 5–6 Mohs; Color: Jet black to dark translucent; 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 translucent
Luster: Vitreous/glassy

Identified March 18, 2026More igneous →

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Physical properties

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

Formation & geological history

Formed through the rapid cooling of felsic (silica-rich) lava, preventing crystal growth. Usually associated with geologically recent volcanic activity (Cenozoic era) due to its tendency to devitrify over time.

Uses & applications

Historically used for cutting tools and weapons (arrowheads/knives); modern use in surgical scalpels, jewelry (cabochons), and ornamental decorative items.

Geological facts

Obsidian edges can be sharpened to nearly molecular thickness, making them sharper than high-quality steel scalpels. This specific specimen has been 'knapped' or flaked manually into a projectile point shape.

Field identification & locations

Identify in the field by its distinct glass-like sheen and sharp, curved fracture lines. Commonly found in volcanic regions such as the American West (Oregon, California), Mexico, and Iceland. Look for edges that are translucent when held to light.

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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)

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Magnetite

Magnetite (Fe3O4)

mineral