igneous

Obsidian

Obsidian (Volcanic Glass, SiO2)

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

Hardness: 5-5
Color: Black, sometimes dark green or brown
Luster: Vitreous/Glassy

Identified June 2, 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. Predominantly found in volcanic areas from the Cenozoic era due to its susceptibility to hydration over long periods.

Uses & applications

Used in the manufacture of surgical scalpel blades, jewelry, decorative ornaments, and historically for sharp tools and weapons like arrowheads.

Geological facts

Obsidian is technically a glass, not a mineral, because it lacks a crystalline structure. Ancient Aztecs used obsidian mirrors for divination and rituals.

Field identification & locations

Identify by its characteristic shiny, glassy appearance and shell-like (conchoidal) fractures with sharp edges. Commonly found in locations like the Western US, Mexico, and Iceland. Collectors look for unique varieties like Snowflake or Mahogany obsidian.

Other igneous specimens

See all

Granite

Igneous

Granite

Igneous

Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

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