igneous
Mahogany Obsidian
Volcanic Glass (High-silica Rhyolite)
Hardness: 5-5.5 (Mohs); Color: Black with reddish-brown streaks or mottling; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like); Specific Gravity: 2.3-2.6
- Hardness
- 5-5
- Color
- Black with reddish-brown streaks or mottling
- Luster
- Vitreous (glassy)
Identified More igneous →
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Physical properties
Hardness: 5-5.5 (Mohs); Color: Black with reddish-brown streaks or mottling; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like); Specific Gravity: 2.3-2.6
Formation & geological history
Forms from the rapid cooling of rhyolitic lava that is too viscous to crystallize. The reddish-brown streaks are caused by inclusions of magnetite or hematite (iron oxide) occurring during the cooling process.
Uses & applications
Used in gemstone carving, jewelry (cabochons and beads), and historically for sharp tools like arrowheads and knives. Also popular in metaphysical collections.
Geological facts
Obsidian fractures with extremely sharp edges, molecularly thinner than a steel scalpel. The 'mahogany' variant gets its name from its resemblance to mahogany wood grain.
Field identification & locations
Identify by its glassy texture, conchoidal fracture patterns, and distinctive reddish-brown bands against a black background. Commonly found in volcanic regions of the Western USA, Mexico, and Japan.
