igneous

Mahogany Obsidian

Volcanic Glass with Hematite/Magnetite inclusions (SiO2)

Hardness: 5-5.5 on Mohs scale; Color: Black with reddish-brown (mahogany) streaks or splotches; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6.

Hardness: 5-5
Color: Black with reddish-brown (mahogany) streaks or splotches
Luster: Vitreous/Glassy

Identified April 4, 2026More igneous →

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Physical properties

Formation & geological history

Formed from rhyolitic volcanic lava that cools rapidly, preventing crystal growth. The mahogany color is specifically caused by inclusions of Hematite or Magnetite during the cooling process.

Uses & applications

Commonly used for lapidary work, jewelry (beads, cabochons), ornamental carvings, and historical tool making (knapping). It is also highly popular in the metaphysical and collecting communities.

Geological facts

Despite having the composition of a mineral, obsidian is technically a volcanic glass because it lacks a crystalline structure. Ancient cultures used mahogany obsidian to make exceptionally sharp arrowheads and blades.

Field identification & locations

Identify by its glassy texture, smooth conchoidal (shell-like) fractures, and distinct reddish-brown swirls within a black base. It is commonly found in areas of recent volcanic activity, particularly in the Western USA, 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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Sodalite

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Magnetite

Magnetite (Fe3O4)

mineral