igneous

Obsidian (Apache Tear)

Volcanic Glass (composed mainly of SiO2)

Hardness: 5.0-5.5 (Mohs); Color: Jet black to smoky dark brown, translucent when held to light; Luster: Vitreous (glassy); Crystal structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.35-2.6

Hardness: 5
Luster: Vitreous (glassy)

Identified March 16, 2026More igneous →

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Physical properties

Formation & geological history

Formed from rapid cooling of high-silica (rhyolitic) lava. These sub-rounded nodules occur when obsidian flows are weathered and hydrated into perlite, leaving original obsidian 'cores' behind.

Uses & applications

Used in ornamental jewelry as tumbled stones, historical use for sharp-edged tools and arrowheads, and used in modern scalpel blades for delicate surgeries due to extreme sharpness.

Geological facts

Legend says Apache Tears were formed from the tears of family members mourning the 1870s defeat of Apache warriors in Arizona. Unlike most rocks, they have no crystalline structure because they cooled too fast for crystals to grow.

Field identification & locations

Identify by holding to a bright light; a true Apache Tear will show a smoky tan or gray transparency. Commonly found in dry, volcanic regions of the Southwestern US, particularly Arizona and New Mexico.

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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