igneous

Mahogany Obsidian

Volcanic glass (SiO2 + Fe2O3)

Hardness: 5-5.5 (Mohs scale); Color: Black with mottled reddish-brown streaks; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6

Hardness: 5-5
Color: Black with mottled reddish-brown streaks
Luster: Vitreous/Glassy

Identified March 25, 2026More igneous →

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Physical properties

Hardness: 5-5.5 (Mohs scale); Color: Black with mottled reddish-brown streaks; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6

Formation & geological history

Formed when rhyolitic lava cools rapidly, preventing crystal growth. The reddish-brown 'mahogany' color is caused by the inclusion of hematite (iron oxide) during rapid solidification within volcanic fields.

Uses & applications

Used primarily for jewelry (cabochons, beads), decorative carvings, and metaphysical collecting. Historically used for making sharp-edged tools and blades.

Geological facts

Unlike minerals, obsidian is a 'mineraloid' because it lacks a crystal structure. Mahogany obsidian is prized for its high-contrast aesthetic compared to standard black obsidian. It has been used for thousands of years by indigenous cultures for ceremonial knives.

Field identification & locations

Identify in the field by its characteristic conchoidal (shell-like) fracture and sharp edges. It is common in volcanic regions like the Glass Buttes in Oregon, USA, and various sites in Mexico. It is softer than quartz and can be scratched by a steel file.

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Igneous