igneous

Mahogany Obsidian

Volcanic Glass (SiO2 + Fe2O3)

Hardness: 5-5.5 on Mohs scale; Color: Reddish-brown with black inclusions; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6.

Hardness: 5-5
Color: Reddish-brown with black inclusions
Luster: Vitreous (glassy)

Identified March 17, 2026More igneous →

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Physical properties

Formation & geological history

Formed from rapidly cooling felsic lava where crystallization does not occur. The 'mahogany' color is caused by the presence of oxidized hematite or magnetite inclusions during the cooling process.

Uses & applications

Used primarily for jewelry (cabochons, beads), decorative carvings, meditation stones, and historically for making sharp tools like arrowheads and scalpel blades.

Geological facts

Despite its appearance, obsidian is a volcanic glass rather than a mineral because it lacks a crystalline structure. Ancient cultures prized it for its ability to produce an edge sharper than surgical steel.

Field identification & locations

Identify in the field by its glassy texture, conchoidal (shell-like) fractures, and distinct brownish-red swirls against black. Commonly found in volcanic regions of Mexico, the United States (Oregon and California), and Japan.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

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