igneous

Mahogany Obsidian

Volcanic Glass (SiO2 + Fe2O3)

Hardness: 5-5.5 (Mohs scale); Color: Dark brown or black with reddish-brown streaks; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.35-2.6.

Hardness: 5-5
Color: Dark brown or black with reddish-brown streaks
Luster: Vitreous/Glassy

Identified May 26, 2026More igneous →

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Physical properties

Formation & geological history

Formed when rhyolitic lava flows cool very quickly, preventing crystal growth. Its distinct reddish-brown color is caused by trace amounts of hematite or magnetite (iron oxide) trapped within the glass. Found in volcanic regions.

Uses & applications

Used primarily for jewelry (cabochons, beads), decorative carvings, and metaphysical healing collections. In pre-history, it was used for razor-sharp tools and weapons.

Geological facts

Obsidian is technically not a mineral but a 'mineraloid' because it lacks a crystal structure. Mahogany obsidian specifically gets its name from the wood-like mahogany color created by iron impurities.

Field identification & locations

Identify by its glass-like texture and characteristic shell-like (conchoidal) fractures. Common in the Western United States (Oregon, California) and Mexico. Collectors should look for distinct reddish mottling against a black background.

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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