igneous

Mahogany Obsidian

Obsidian (Volcanic Glass) with Hematite/Magnetite inclusions

Hardness: 5-5.5 (Mohs); Color: Dark brown or reddish-brown with black spots; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6

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

Identified March 25, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the extremely rapid cooling of felsic lava, preventing crystal growth. Its reddish-brown color is caused by the inclusion of iron-rich minerals like hematite or magnetite during the cooling process. Usually found in geologically recent volcanic areas (Cenozoic era).

Uses & applications

Commonly used in jewelry, lapidary arts (cabochons and beads), and decorative carvings. Historically, obsidian was used for sharp cutting tools and surgical blades; currently popular in the metaphysical and gemstone collecting markets.

Geological facts

Obsidian is often called 'volcanic glass.' While it looks like a mineral, it is technically an 'extrusive igneous rock' because it lacks a crystalline structure. The 'Mahogany' variety is prized for its wavy, wood-grain-like patterns.

Field identification & locations

Identify by its glass-like texture, conchoidal (shell-like) fracture patterns, and its distinct red-and-black mottling. Commonly found in volcanic regions of the Western United States (Oregon, California), Mexico, 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

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