igneous

Obsidian

Obsidian (Amorphous volcanic glass, SiO2 with impurities)

Hardness: 5-5.5 (Mohs scale); Color: Black, deep brown, or grey; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (shows conchoidal fracture); Specific Gravity: 2.3-2.6

Hardness: 5-5
Color: Black, deep brown, or grey
Luster: Vitreous/Glassy

Identified February 14, 2026More igneous →

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Physical properties

Hardness: 5-5.5 (Mohs scale); Color: Black, deep brown, or grey; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (shows conchoidal fracture); Specific Gravity: 2.3-2.6

Formation & geological history

Formed through the rapid cooling of silica-rich (felsic) lava, which prevents crystal growth. It appears in volcanic regions from various geological eras, primarily the Cenozoic era due to its susceptibility to devitrification over time.

Uses & applications

Used historically for cutting tools, scalpels, and arrowheads. Modern uses include surgical blades (due to its molecular edge sharpness), jewelry (cabochons/beads), and ornamental carvings.

Geological facts

Because it is a glass and not a crystal, it is technically a 'mineraloid.' It is so sharp that its edge can be thinner than a high-quality steel scalpel. Native Americans traded this extensively across North American trade routes.

Field identification & locations

Identify in the field by its characteristic 'conchoidal' (shell-like) fracture patterns and extremely sharp edges. Commonly found in Oregon, California, Iceland, and Mexico near rhyolitic volcanic sites. Collectors should look for unique sheen or 'snowflakes'.

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