igneous

Obsidian

Volcanic Glass (Primary composition: SiO2 - Silicon Dioxide)

Hardness: 5-6 on Mohs scale; Color: typically jet black, can be dark green or brown; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6

Hardness: 5-6 on Mohs scale
Color: typically jet black, can be dark green or brown
Luster: Vitreous (glassy)

Identified March 28, 2026More igneous →

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Physical properties

Formation & geological history

Formed from rapidly cooling extrusive felsic lava where crystals lack the time to grow. Most found today are relatively young geologically (less than 65 million years old) because it eventually devitrifies into stable minerals.

Uses & applications

Used historically for arrowheads and blades; modernly used for scalpel blades in heart surgery, ornamental jewelry, carvings, and as a protective gemstone in metaphysical communities.

Geological facts

Obsidian is so sharp that its edge can be thinner than a molecule of steel, potentially down to 3 nanometers. It is not technically a mineral because it lacks a crystalline structure.

Field identification & locations

Identify in the field by its smooth, glassy texture and distinctive 'c-shaped' conchoidal fractures. Common in volcanic regions such as Oregon (Glass Buttes), California, Iceland, and Mexico.

Other igneous specimens

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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