igneous

Black Obsidian

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

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

Hardness: 5-5
Color: Jet black
Luster: Vitreous/Glassy

Identified March 28, 2026More igneous →

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Physical properties

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

Formation & geological history

Formed from extrusive igneous activity when felsic lava cools rapidly with minimum crystal growth. It is relatively young geologically (usually Cenozoic) because it eventually devitrifies into quartz and feldspar crystals.

Uses & applications

Used primarily in jewelry and ornamental carvings. Historically used for extremely sharp cutting tools, blades, and arrowheads. Also used in modern medicine for high-precision surgical scalpel blades.

Geological facts

Obsidian is technically a glass, not a mineral, because it lacks an internal crystalline structure. It was highly prized by the Aztecs and Mayans for mirrors and sacrificial daggers.

Field identification & locations

Identify in the field by its characteristic conchoidal (shell-like) fracture patterns and sharp edges. It is commonly found in volcanic regions such as the American Northwest (Oregon, California), Mexico, Iceland, and Italy.

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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