igneous

Mahogany Obsidian

Volcanic Glass (with inclusions of Magnetite or Hematite)

Hardness: 5.0-5.5 on Mohs scale; Color: Reddish-brown to black with wavy or spotted patterns; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.60

Hardness: 5
Color: Reddish-brown to black with wavy or spotted patterns
Luster: Vitreous (glassy)

Identified May 18, 2026More igneous →

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Physical properties

Formation & geological history

Formed when felsic lava high in silica cools extremely rapidly, preventing crystal growth. Its mahogany color comes from high concentrations of iron oxide and hematite. It can be found in volcanic regions spanning millions of years to recent history.

Uses & applications

Used primarily for lapidary work, jewelry making (cabochons and beads), ornamental carvings, and historical sharp tools/weapons. It is also a popular specimen for rock collection and metaphysical uses.

Geological facts

Mahogany Obsidian is unique because it is technically a glass rather than a mineral. In ancient times, obsidian was prized more for its ability to be flaked into blades sharper than steel than for its beauty.

Field identification & locations

Identify by its glass-like texture, conchoidal (shell-like) fracture patterns, and distinctive dark 'blobs' of brown iron oxide within a black or tan background. Commonly found in Oregon (USA), Mexico, and volcanic areas of 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

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral