igneous

Black Obsidian

Volcanic Glass (Primary composition: SiO2 - Silicon Dioxide)

Hardness: 5.0 - 6.0 on Mohs scale; Color: Jet black to dark grayish; Luster: Vitreous (glassy); Crystal structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.35 - 2.6

Hardness: 5
Color: Jet black to dark grayish
Luster: Vitreous (glassy)

Identified March 11, 2026More igneous →

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Physical properties

Formation & geological history

Formed from rapid cooling of high-silica felsic lava (rhyolitic) which prevents crystal growth. It is found in volcanic regions of various ages, particularly the Cenozoic era.

Uses & applications

Used in gemstone jewelry (cabochons), ornamental decorative items, and historically for ultra-sharp surgical blades and prehistoric tools like spearheads.

Geological facts

Because it is a glass rather than a true mineral, it is technically a 'mineraloid'. It breaks with extremely sharp edges—thinner than a steel scalpel—and was favored by the Maya and Aztecs for weaponry.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture and smooth, glassy surface. Commonly found in locations like Yellowstone (USA), Iceland, Mexico, and Japan.

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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)

mineral

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral