Igneous

Rainbow Obsidian

Volcanic Glass (SiO2 + impurities)

Hardness: 5-5.5 (Mohs); Color: Black with iridescent multicolored sheen; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific Gravity: 2.35-2.6

Hardness: 5-5
Color: Black with iridescent multicolored sheen
Luster: Vitreous/Glassy

Identified March 28, 2026More igneous →

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Physical properties

Hardness: 5-5.5 (Mohs); Color: Black with iridescent multicolored sheen; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific Gravity: 2.35-2.6

Formation & geological history

Formed from the rapid cooling of silica-rich rhyolitic lava. The 'rainbow' effect is caused by tiny inclusions of magnetite or oriented nanoparticles/bubbles trapped during the cooling process.

Uses & applications

Primarily used for lapidary work, jewelry (cabochons), pocket stones, and decorative carvings. Historically used for sharp cutting tools and arrowheads.

Geological facts

Obsidian is technically a supercooled liquid rather than a true mineral because it lacks a crystalline structure. The rainbow effect is most visible when the stone is wet or polished and held under a bright direct light source.

Field identification & locations

Identify by its glassy texture, shell-like (conchoidal) fracture pattern, and the subtle, concentric 'eye' layers of color. Commonly found in volcanic regions such as Oregon, Mexico, and Iceland.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral