igneous

Black Obsidian

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

Hardness: 5–5.5 on Mohs scale; Color: Jet black to dark gray; Luster: Vitreous (glass-like); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4

Hardness: 5–5
Color: Jet black to dark gray
Luster: Vitreous (glass-like)

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 felsic lava, preventing crystal growth. Most specimens found today are relatively young geologically (Cenozoic to Holocene) as the glass eventually devitrifies into quartz and feldspar over millions of years.

Uses & applications

Used for making jewelry, scalpels for precision surgery due to its molecularly sharp edges, ornamental carvings, and 'scrying' stones in metaphysical communities.

Geological facts

Because it lacks a crystal structure, obsidian edges can reach near-molecular thinness, making it sharper than high-quality steel scalpels. It was used by ancient civilizations for weaponry, such as the Aztec Macuahuitl.

Field identification & locations

Identify by its smooth, glassy surface and characteristic curved (conchoidal) fractures that resemble ripples in water. Commonly found in volcanic regions such as the American Northwest, Mexico, Iceland, and Italy.

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