igneous
Polished mahogany obsidian (probable)
Volcanic glass; mostly amorphous silica (SiO₂) with iron-oxide inclusions
AI-generated identification · may be incorrectDark brown to black, glossy vitreous luster with mottled reddish-brown patches; conchoidal fracture and no cleavage. Mohs hardness about 5–5.5; typically opaque, with specific gravity around 2.3–2.6. The specimen is shaped and polished, so natural fracture surfaces are absent.
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Physical properties
Dark brown to black, glossy vitreous luster with mottled reddish-brown patches; conchoidal fracture and no cleavage. Mohs hardness about 5–5.5; typically opaque, with specific gravity around 2.3–2.6. The specimen is shaped and polished, so natural fracture surfaces are absent.
Formation & geological history
Forms when silica-rich lava cools so rapidly that crystals cannot grow, commonly in volcanic domes and flows; its age varies from Pleistocene to recent depending on locality. Brown coloration reflects microscopic iron-oxide-rich inclusions or flow textures.
Uses & applications
Used for ornamental objects, cabochons, beads, carvings, and lapidary specimens; historically fashioned into sharp tools and arrowheads.
Geological facts
Mahogany obsidian is a variety of obsidian distinguished by brown or reddish patches within black glass. It can resemble mahogany jasper, which is opaque and microcrystalline rather than glassy.
Field identification & locations
Look for glassy polish, lightweight feel, conchoidal edges, and lack of visible crystals; a strong flashlight may reveal slight translucence at thin edges. Common sources include Mexico, the western United States, and Armenia.
