igneous
Mahogany Obsidian
Volcanic glass (SiO2 with Hematite or Magnetite inclusions)
Hardness: 5-5.5 (Mohs), Color: Black with reddish-brown streaks/spots, Luster: Vitreous/Glassy, Crystal Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture)
- Hardness
- 5-5
Identified More igneous →
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Physical properties
Hardness: 5-5.5 (Mohs), Color: Black with reddish-brown streaks/spots, Luster: Vitreous/Glassy, Crystal Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture)
Formation & geological history
Formed when rhyolitic volcanic lava cools very rapidly, preventing crystal growth. The mahogany coloration comes from inclusions of magnetite or hematite during the cooling process.
Uses & applications
Commonly used for lapidary work, jewelry (beads, cabochons), ornamental carvings, and historically used for making extremely sharp cutting tools/blades.
Geological facts
Obsidian fractures with edges that can be thinner and sharper than a surgical steel scalpel. The brown patterns in Mahogany Obsidian are often needle-like inclusions of iron minerals.
Field identification & locations
Identify by its glass-like texture and characteristic conchoidal (shell-like) fracture patterns. Frequently found in volcanic areas of the Western United States, Mexico, and Japan.
