igneous

Mahogany Obsidian Arrowhead

Obsidian (volcanic glass) with Hematite inclusions

Hardness: 5-5.5 (Mohs); Color: Reddish-brown and black streaks; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4

Hardness: 5-5
Color: Reddish-brown and black streaks
Luster: Vitreous/Glassy

Identified April 6, 2026More igneous →

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Physical properties

Hardness: 5-5.5 (Mohs); Color: Reddish-brown and black streaks; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4

Formation & geological history

Formed from the rapid cooling of felsic lava, preventing crystal growth. The mahogany color is caused by the inclusion of magnetite or hematite during the cooling process.

Uses & applications

Historically used for weaponry and tools; currently used in jewelry, ornamental carvings, lapidary arts, and as a collector's item.

Geological facts

Obsidian fractures with extremely sharp edges, historically used for surgical blades. Mahogany obsidian is specifically prized for its 'wood-grain' appearance.

Field identification & locations

Identify in the field by its glassy texture, shell-like (conchoidal) fracture patterns, and lack of visible crystals. Found in volcanic regions like the Western United States, Mexico, and Japan.

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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)

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Magnetite

Magnetite (Fe3O4)

mineral