igneous

Obsidian (Black)

Obsidian (approx. 70–75% SiO2)

Hardness: 5–6 Mohs Scale; Color: Jet black; Luster: Vitreous/Glossy; Structure: Amorphous (glassy, no crystal structure); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4

Hardness: 5–6 Mohs Scale
Color: Jet black
Luster: Vitreous/Glossy

Identified March 20, 2026More igneous →

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Physical properties

Hardness: 5–6 Mohs Scale; Color: Jet black; Luster: Vitreous/Glossy; Structure: Amorphous (glassy, no crystal structure); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4

Formation & geological history

Formed as an extrusive igneous rock when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Common in areas of geologically recent volcanic activity (Cenozoic era).

Uses & applications

Used historically for sharp cutting tools/scalpels; currently used in jewelry (cabochons), ornamental carvings, and for meditation/metaphysical collections.

Geological facts

Because it is a glass and not a crystal, obsidian is metastable and will eventually devitrify into quartz and feldspar over millions of years. This is why few obsidian specimens are older than the Cretaceous period.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture and sharp edges. Common in volcanic regions like the American West (Glass Buttes, OR), Iceland, and Mexico. Collectors should look for a uniform, glass-like transparency on thin edges.

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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