igneous

Obsidian (in jewelry setting)

Volcanic Glass (Amorphous Silica)

Hardness: 5-5.5 (Mohs scale); Color: Typically deep black (due to iron and magnesium); Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.3 - 2.6.

Hardness: 5-5
Color: Typically deep black (due to iron and magnesium)
Luster: Vitreous/Glassy

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, which prevents the growth of mineral crystals. It is common in volcanically active regions and is generally geologically young (less than 65 million years) as glass eventually devitrifies.

Uses & applications

Used primarily for jewelry, ornamental objects, and surgical scalpel blades (due to its ability to be honed to an edge much sharper than steel). It is also highly valued by gemstone collectors and for decorative metaphysical items.

Geological facts

Because it breaks with a conchoidal fracture, it creates edges that are molecularly thin. In the Stone Age, it was the primary material for high-quality arrowheads and blades. It shares the same chemical composition as granite but cooled too fast to crystallize.

Field identification & locations

Identify in the field by its characteristic glassy texture and curved, shell-like (conchoidal) fractures. Found in volcanic areas with silica-rich lava such as the Western USA, Mexico, Iceland, and Japan. Collectors 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

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