igneous

Obsidian

Volcanic Glass (SiO2 rich)

Hardness: 5-5

Identified February 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

Obsidian forms when silica-rich felsic lava cools extremely rapidly, which prevents the growth of crystals. It is typically found in volcanic regions of various ages, though it can devitrify over millions of years into more stable minerals.

Uses & applications

Historically used for surgical blades and knapping into sharp tools/weapons (arrows, spears); currently used in jewelry (beads, cabochons), modern scalpels for precision surgery, and as a popular collector's stone.

Geological facts

Because it's a glass, it breaks with sharp edges like a razor, down to a single molecule thick. In many cultures, like the Aztecs and Mayans, it was a vital trade commodity for making ceremonial knives and mirrors.

Field identification & locations

Identify in the field by its distinct conchoidal (shell-like) fracture pattern and extremely glossy, smooth surface. It is commonly found in the Pacific Northwest (USA), Mexico, Iceland, and Japan. Collectors should look for unique variations like 'Snowflake' or 'Rainbow' obsidian.

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