igneous

Mahogany Obsidian

Obsidian (SiO2 + Fe2O3)

Hardness: 5-5.5 (Mohs scale); Color: Black with reddish-brown streaks or patches; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6

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

Identified March 2, 2026More igneous →

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Physical properties

Formation & geological history

Formed from rapidly cooling felsic lava that contains high levels of silica. The red-brown streaks are caused by inclusions of Hematite or Magnetite (iron oxide). It is typically found in volcanic regions of various geological ages from the Cenozoic era.

Uses & applications

Commonly used in jewelry for beads and cabochons, decorative carvings, and in alternative medicine practices (metaphysical healing). Historically, obsidian was used to make sharp cutting tools.

Geological facts

Unlike minerals, obsidian is a 'mineraloid' because it lacks a crystal structure. Mahogany obsidian specifically gets its name from its similarity to the color of mahogany wood due to the iron-rich inclusions.

Field identification & locations

Identify by its glassy texture and distinct reddish-brown rhythmic swirling or spotting against a dark background. It is commonly found in the United States (Oregon, California), Mexico, and Japan.

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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