igneous
Mahogany Obsidian
Volcanic Glass (SiO2 with Hematite/Magnetite inclusions)
Hardness: 5-5.5 Mohs scale. Color: Reddish-brown/mahogany streaks mixed with black. Luster: Vitreous to glassy. Structure: Amorphous (non-crystalline glass). Cleavage: None, exhibits conchoidal fracture.
- Hardness
- 5-5
- Color
- Reddish-brown/mahogany streaks mixed with black
- Luster
- Vitreous to glassy
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Physical properties
Hardness: 5-5.5 Mohs scale. Color: Reddish-brown/mahogany streaks mixed with black. Luster: Vitreous to glassy. Structure: Amorphous (non-crystalline glass). Cleavage: None, exhibits conchoidal fracture.
Formation & geological history
Formed when felsic lava rich in silica cools rapidly with minimal crystal growth. The reddish-brown swirls or spots are caused by inclusions of hematite or magnetite during formation.
Uses & applications
Widely used in jewelry making (beads, cabochons, carvings), decorative items, and lapidary practice. Historically used for sharp tools and arrowheads.
Geological facts
Mahogany Obsidian gets its characteristic reddish hue from iron impurities (specifically hematite). Because it is a natural glass rather than a true mineral, it has no internal crystal lattice.
Field identification & locations
Identified by its rich reddish-brown and black swirled or splotched appearance, glassy texture, and smooth conchoidal fractures. Commonly found in volcanic regions such as Oregon (USA), Mexico, Japan, and Armenia.
