igneous

Black Obsidian

Volcanic Glass (predominantly SiO2)

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

Hardness: 5–5
Color: Jet black to dark gray
Luster: Vitreous (glassy)

Identified February 9, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of felsic lava, which prevents the growth of crystals. It is typically found in volcanic regions with high silica content, often dating from the Neogene to Quaternary periods.

Uses & applications

Used for ornamental carvings, jewelry (cabochons and beads), and historically for extremely sharp scalpel blades and hunter-gatherer tools like arrowheads.

Geological facts

Because it is a glass rather than a true mineral, it is chemically unstable over long geological time and eventually 'devitrifies' into quartz crystals. It has been used since the Stone Age for its sharp edges, which can be thinner than steel.

Field identification & locations

Identify by its characteristic glassy sheen and razor-sharp conchoidal (curved) edges when broken. It feels lighter than many dark minerals. Commonly found in places like Mexico, the American West, and Iceland.

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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