igneous

Obsidian (Black Obsidian)

Obsidian (Volcanic Glass)

Hardness: 5–5.5 Mohs; Color: Jet black; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4

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

Identified April 4, 2026More igneous →

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Physical properties

Hardness: 5–5.5 Mohs; Color: Jet black; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4

Formation & geological history

Formed from rapid cooling of felsic (silica-rich) lava, preventing crystal growth. Usually found in geologically recent volcanic fields (often less than 20 million years old because it eventually devitrifies).

Uses & applications

Used for making ultra-sharp surgical scalpels, decorative jewelry (cabochons), and ornamental carved objects. Historically used for arrowheads and daggers.

Geological facts

Obsidian fractures with extremely sharp edges—thinner than a steel scalpel—which allows for cleaner incisions and faster healing in certain medical procedures. It is technically a 'mineraloid' rather than a mineral because it lacks a crystalline structure.

Field identification & locations

Identify by its glassy texture and distinctive shell-like (conchoidal) fracture pattern when chipped. Found globally in volcanic regions like Iceland, Mexico, and the Western United States (Oregon, California).

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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