igneous

Black Obsidian

Obsidian (Volcanic Glass), primarily SiO2 (Silicon Dioxide)

Hardness: 5-5.5 (Mohs scale); Color: Jet black to dark brownish-black; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6.

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

Identified March 25, 2026More igneous →

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Physical properties

Formation & geological history

Formed when silica-rich lava cools so rapidly that crystals do not have time to grow. It is extrusive igneous rock, typically found in areas with geologically recent volcanic activity (Cenozoic era).

Uses & applications

Historically used for arrowheads and blades; currently used in jewelry (beads and cabochons), ornamental carvings, and specialized surgical scalpels due to its ability to produce an edge thinner than steel.

Geological facts

Because it is a glass rather than a true mineral, it is chemically unstable over millions of years and eventually devitrifies (turns into rock). It can produce a cutting edge that is molecularly thin.

Field identification & locations

Identify by its glassy texture, deep black color, and distinctive shell-like (conchoidal) fracture patterns. Found commonly in volcanic regions like the American West (Oregon, California, Iceland, and Mexico).

Other igneous specimens

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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