igneous

Obsidian

Obsidian (Volcanic Glass)

Hardness: 5–5.5 (Mohs scale), Color: Jet black to dark grey, Luster: Vitreous/Glassy, Crystal Structure: Amorphous, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.35–2.6

Hardness: 5–5

Identified May 10, 2026More igneous →

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Physical properties

Hardness: 5–5.5 (Mohs scale), Color: Jet black to dark grey, Luster: Vitreous/Glassy, Crystal Structure: Amorphous, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.35–2.6

Formation & geological history

Formed through the rapid cooling of silica-rich (felsic) lava, which prevents crystal growth. Usually relatively young geologically (Cretaceous to Holocene) because it eventually devitrifies into crystalline rock.

Uses & applications

Used for surgical scalpel blades, ornamental jewelry, decorative carvings, and historically for sharp tools like arrowheads and knives.

Geological facts

Obsidian is not a mineral because it lacks a crystalline structure; it is considered a mineraloid. Known as 'Dragon Glass' in popular culture, it has been traded by humans for thousands of years.

Field identification & locations

Identify by its extremely smooth, glass-like surface and sharp conchoidal (shell-like) fractures. Common in volcanic regions such as the American Northwest, Iceland, Mexico, and Japan.

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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