igneous

Obsidian

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

Hardness: 5-5.5 on Mohs scale; Color: typically black but can show sheen or translucency; Luster: Vitreous (glassy); Crystal Structure: Amorphous (lacks crystal structure); Cleavage: Conchoidal fracture

Hardness: 5-5
Color: typically black but can show sheen or translucency
Luster: Vitreous (glassy)

Identified March 14, 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 extremely rapid cooling of felsic lava, which prevents the growth of crystals. It is found in geologically young areas with recent volcanic activity, predominantly from the Cenozoic era.

Uses & applications

Used historically for sharp tools and weapons (scalpels, arrowheads). In modern times, it is used for jewelry, decorative carvings, gemstones, and as a high-quality material for surgical blades.

Geological facts

Because it has no crystal structure, obsidian can be honed to an edge only a few molecules thick, making it sharper than even the finest steel surgical blades. It is also known as 'Dragon Glass' in popular culture (Game of Thrones).

Field identification & locations

Identify in the field by its distinctive glassy appearance and shell-like (conchoidal) fractures. Common locations include the Western USA (Oregon, California), Mexico, Iceland, and Italy. Collectors look for specific optical effects like 'sheen' or 'snowflake' patterns.

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

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral