igneous

Mahogany Obsidian

Volcanic glass containing Hematite or Magnetite (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 17, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of rhyolitic lava that is rich in silica and iron. The reddish-brown color is caused by the presence of oxidized hematite or magnetite inclusions during cooling. Most specimens are from the Cenozoic era.

Uses & applications

Used primarily in lapidary work for jewelry (cabochons, beads), decorative carvings, and metaphysical collecting. Historically used for sharp tools and arrowheads.

Geological facts

Obsidian is technically a 'mineraloid' rather than a mineral because it lacks a crystal structure. Mahogany obsidian is prized for its unique 'wood-grain' pattern, which makes every piece unique.

Field identification & locations

Identify in the field by its distinctive glassy appearance and sharp, curved (conchoidal) edges. It is commonly found in volcanic regions of Mexico, the United States (Oregon, California), and Japan.

Other igneous specimens

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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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral