Igneous

Mahogany Obsidian

Volcanic Glass with Hematite/Magnetite inclusions (SiO2 + Fe2O3)

Hardness: 5-5.5 (Mohs scale); Color: Black with mottled streaks or splotches of reddish-brown; Luster: Vitreous (glassy); Crystal structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.3-2.6

Hardness: 5-5
Color: Black with mottled streaks or splotches of reddish-brown
Luster: Vitreous (glassy)

Identified March 22, 2026More igneous →

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Physical properties

Formation & geological history

Formed from extrusive volcanic activity where felsic lava cools rapidly with minimal crystal growth. The mahogany color is caused by the inclusion of iron oxides (hematite or magnetite) that become trapped during the cooling process. Most specimens are relatively young geologically, typically from the Cenozoic era.

Uses & applications

Commonly used for lapidary work, including spheres (like the one pictured), cabochons, and beads. It is also used in decorative carvings, feng shui practices, and increasingly in surgical scalpel manufacturing due to its ability to create an edge thinner than steel.

Geological facts

Because it has no crystal structure, obsidian breaks with extremely sharp, curved edges. For millennia, it was the preferred material for making spearheads and arrowheads. Mahogany obsidian is considered one of the 'gentler' forms of obsidian in metaphysical circles.

Field identification & locations

Identify in the field by its glassy texture and distinctive conchoidal (shell-like) fracture patterns. It is found in areas of recent volcanic activity, most notably in the United States (Oregon, Utah, Arizona, California), Mexico, and Japan. Collectors look for high contrast between the red and black bands.

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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.

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Magnetite

Iron(II,III) oxide (Fe3O4)

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Sodalite

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Magnetite

Magnetite (Fe3O4)

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