igneous

Obsidian

Obsidian (Volcanic Glass), primarily SiO2 (Silicon Dioxide)

Hardness: 5-5.5 on Mohs scale; Color: Black to deep brown (may show sheen or rainbow effects); Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6.

Hardness: 5-5
Color: Black to deep brown (may show sheen or rainbow effects)
Luster: Vitreous (glassy)

Identified March 15, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through the rapid cooling of silica-rich (felsic) lava, which prevents the growth of crystals. It is found in geologically young volcanic areas, as it is unstable over long geological time and eventually devitrifies into quartz and feldspar.

Uses & applications

Used historically for sharp tools and weapons (arrowheads, blades); modern uses include surgical scalpels for ultra-fine incisions, decorative jewelry, cabochons, and metaphysical 'protection' stones.

Geological facts

Obsidian is often called 'Nature's Glass.' Because it lacks a crystal structure, its edges can reach near-molecular thinness, making it sharper than even high-quality steel surgical scalpels.

Field identification & locations

Identify in the field by its distinctive conchoidal (shell-like) fracture patterns and sharp edges. Common locations include the Western USA (Oregon, California), Mexico, Iceland, and Japan. Collectors look for unique optical effects like gold or silver sheen and rainbow bands.

Other igneous specimens

See all

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