igneous

Mahogany Obsidian

Obsidian (Volcanic Glass) with Hematite/Magnetite inclusions

Hardness: 5.0-5.5 on Mohs scale; Color: Black with reddish-brown streaks; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6.

Hardness: 5
Color: Black with reddish-brown streaks
Luster: Vitreous (glassy)

Identified March 17, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of silica-rich (rhyolitic) lava, which prevents crystal growth. The mahogany color comes from magnetite or hematite inclusions during the cooling process, typically found in volcanic fields varying from thousands to millions of years old.

Uses & applications

Used primarily in lapidary for making beads, cabochons, and jewelry. It is also highly popular in 'crystal healing' communities and as a display specimen for collectors.

Geological facts

Obsidian was historically used to make some of the sharpest cutting tools and arrowheads in human history. Mahogany obsidian is chemically similar to black obsidian but differs due to the oxidation of iron within the glass during its formation.

Field identification & locations

Identify in the field by its distinctive glassy, rippled (conchoidal) surface and reddish-brown mottling. It is commonly found in the United States (Oregon, California, Utah), Mexico, and Japan.

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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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Magnetite

Magnetite (Fe3O4)

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