igneous

Mahogany Obsidian

Obsidian (Volcanic Glass with Hematite/Magnetite inclusions), SiO2

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

Hardness: 5-5
Color: Black with reddish-brown streaks or mottling
Luster: Vitreous/Glassy

Identified March 25, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed from rapidly cooling extrusive igneous lava, specifically rhyolitic lava. The mahogany color comes from the inclusion of iron oxides (Hematite or Magnetite) during the cooling process. Common in Pliocene to Holocene volcanic fields.

Uses & applications

Used primarily in jewelry-making for cabochons and beads, as a lapidary material for decorative carvings, and in metaphysical practices. Historically used to craft sharp blades and arrowheads.

Geological facts

Despite looking like a mineral, it is actually a 'mineraloid' because it lacks a crystalline structure. The reddish-brown 'mahogany' swirls are essentially rusted iron trapped within the volcanic glass.

Field identification & locations

Identify by its glass-like texture, sharp conchoidal edges when broken, and distinctive brick-red patterns against a black base. Commonly found in North America (USA-Oregon, Mexico), Japan, and Afghanistan.

Other igneous specimens

See all

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