igneous

Obsidian

Volcanic Glass (SiO2)

Hardness: 5-5.5; Color: Jet black, dark brown, or gray; Luster: Vitreous/glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4

Hardness: 5-5
Color: Jet black, dark brown, or gray
Luster: Vitreous/glassy

Identified February 19, 2026More igneous →

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Physical properties

Hardness: 5-5.5; Color: Jet black, dark brown, or gray; Luster: Vitreous/glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4

Formation & geological history

Formed when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Common in young volcanic areas (Cenozoic era) because it becomes unstable over millions of years.

Uses & applications

Used for making surgical scalpel blades, ornamental jewelry (beads, cabochons), and mirrors. Historically used for weapons like arrowheads and knives.

Geological facts

Obsidian is technically a supercooled liquid rather than a true mineral because it lacks a crystalline structure. It is one of the sharpest materials known to science when fractured.

Field identification & locations

Identify by its smooth, glassy surface and distinctive curved (conchoidal) fractures. Found in volcanic regions like the American West (Glass Buttes), Mexico, and Iceland.

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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