igneous

Black Obsidian

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

Hardness: 5–5.5 (Mohs scale); Color: Jet black to dark grey; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6

Hardness: 5–5
Color: Jet black to dark grey
Luster: Vitreous/Glassy

Identified March 20, 2026More igneous →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 5–5.5 (Mohs scale); Color: Jet black to dark grey; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6

Formation & geological history

Formed through the rapid cooling of silica-rich (felsic) lava from volcanic eruptions, preventing crystal growth. Most specimens found today are from the Quaternary period (less than 2.6 million years old).

Uses & applications

Used historically for sharp tools and weapons (arrowheads/knives); currently used for jewelry, decorative carvings, scalpel blades in specialized surgery, and metaphysical collecting.

Geological facts

Obsidians are technically 'frozen liquids' rather than true minerals because they lack a crystal structure. Ancient civilizations like the Aztecs and Mayans used polished obsidian as mirrors and currency.

Field identification & locations

Identify by its distinctive shell-like (conchoidal) fracture and sharp edges. Commonly found in volcanic regions such as the American West (Oregon, California), Mexico, Iceland, and Japan.

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