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
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Physical properties
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
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.
