igneous

Mahogany Obsidian

Volcanic Glass with Hematite/Magnetite (SiO2 + Fe2O3)

Hardness: 5–5.5 Mohs. Color: Black with reddish-brown streaks or mottling. Luster: Vitreous (glassy). Crystal Structure: Amorphous. Cleavage: None (conchoidal fracture). Specific Gravity: 2.35–2.60.

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

Identified March 25, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of felsic lava, preventing mineral crystallization. The distinctive mahogany color is caused by the inclusion of iron oxides (hematite or magnetite) during the cooling process in volcanic environments.

Uses & applications

Primarily used in jewelry (beads, cabochons), ornamental carvings, and holistic stone collecting. Historically used for making sharp tools like arrows and scrapers due to its conchoidal fracture.

Geological facts

Despite looking like a mineral, obsidian is actually a volcanic glass. Mahogany obsidian is rarer than pure black obsidian and is highly prized for its unique undulating patterns that look like wood grain.

Field identification & locations

Identify by its glass-like texture and red-brown swirls against a black background. Commonly found in areas with recent volcanic activity such as the Western USA (Oregon, California), Mexico, and Japan. Best identified by its smooth, sharp edges when broken.

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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

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Blue Apatite

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

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Magnetite

Magnetite (Fe3O4)

mineral