igneous

Obsidian

Obsidian (Volcanic Glass, SiO2 + impurities)

Hardness: 5-5.5 on Mohs scale. Color: Black (shown), also green, brown, or gold sheen. Luster: Vitreous/Glassy. Structure: Amorphous (non-crystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.35-2.6.

Hardness: 5-5
Color: Black (shown), also green, brown, or gold sheen
Luster: Vitreous/Glassy

Identified March 11, 2026More igneous →

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Physical properties

Formation & geological history

Formed from rapid cooling of felsic (silica-rich) lava, preventing crystal growth. It is found in geologically young areas due to its tendency to devitrify over time.

Uses & applications

Used in surgical scalpel blades for extreme sharpness, ornamental jewelry (cabochons and beads), construction as a raw material for rock wool, and highly valued by lapidary collectors.

Geological facts

Ancient cultures used obsidian for projectile points and mirrors. It is technically a 'mineraloid' rather than a mineral because it lacks a crystalline structure. It is essentially frozen liquid.

Field identification & locations

Identify in the field by its characteristic conchoidal fracture (curved, shell-like breaks) and sharp edges. Commonly found in volcanic regions like the American West (Oregon, California), Mexico, and Iceland.

Other igneous specimens

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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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral