igneous
Mahogany Obsidian
Volcanic glass (SiO2 with Fe2O3 inclusions)
AI-generated identification · may be incorrectMohs hardness: 5.0-5.5; Color: black with reddish-brown streaks; Luster: vitreous (glassy); Structure: amorphous; Cleavage: none; Fracture: conchoidal; Specific Gravity: 2.35-2.6.
- Hardness
- 5
- Color
- black with reddish-brown streaks
- Luster
- vitreous (glassy)
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Physical properties
Mohs hardness: 5.0-5.5; Color: black with reddish-brown streaks; Luster: vitreous (glassy); Structure: amorphous; Cleavage: none; Fracture: conchoidal; Specific Gravity: 2.35-2.6.
Formation & geological history
Formed when felsic lava cools rapidly with minimal crystal growth. The reddish-brown 'mahogany' patterns are caused by inclusions of hematite or magnetite (iron oxides) during the rapid cooling process.
Uses & applications
Used for making jewelry cabochons, decorative carvings, metaphysical tools, and historically for sharp-edged tools like blades or arrowheads.
Geological facts
Obsidian is more of a supercooled liquid than a true mineral because it lacks a crystalline structure. Ancient civilizations valued it for its ability to be fractured into edges thinner and sharper than a surgeon's scalpel.
Field identification & locations
Identified by its signature glassy texture and the swirling reddish-brown patterns against a black base. It is commonly found in volcanic regions such as the United States (Oregon, California), Mexico, and Japan.
