igneous

Obsidian

Volcanic glass (high silica volcanic rock)

Hardness: 5-5.5 (Mohs scale); Color: Black with hints of grey/white (snowflake inclusions possible); Luster: Vitreous/glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35-2.6

Hardness: 5-5
Luster: Vitreous/glassy

Identified March 15, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of silica-rich (rhyolitic) lava, preventing crystal growth. It exists in young volcanic regions because it eventually devitrifies into crystalline rock over millions of years.

Uses & applications

Used in the manufacture of surgical scalpels (sharper than steel), ornamental carvings, gemstones for jewelry, and historically for arrowheads and cutting tools.

Geological facts

Obsidian is not a mineral because it lacks a crystalline structure; it is considered a 'mineraloid.' It was one of the most significant trade items in the Neolithic and Bronze eras due to its razor-sharp edges.

Field identification & locations

Identify in the field by its distinct glassy appearance and conchoidal fracture (curved, sharp glass-like breaks). Common in volcanic areas like the Western United States (Oregon, California), Mexico, and Iceland. Look for extremely sharp edges.

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

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral