igneous
Scoria
Extrusive Basaltic Scoria
Hardness: 5-6 Mohs. Color: Dark gray, black, reddish-brown. Luster: Dull. Texture: Highly vesicular (honeycomb-like). Crystal Structure: Aphanitic (fine-grained), often glass-dominated. Specific Gravity: 0.8 to 2.0 (often floats briefly)
- Hardness
- 5-6 Mohs
- Color
- Dark gray, black, reddish-brown
- Luster
- Dull
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Physical properties
Hardness: 5-6 Mohs. Color: Dark gray, black, reddish-brown. Luster: Dull. Texture: Highly vesicular (honeycomb-like). Crystal Structure: Aphanitic (fine-grained), often glass-dominated. Specific Gravity: 0.8 to 2.0 (often floats briefly)
Formation & geological history
Formed from gassy, mafic magma ejected during explosive volcanic eruptions. As the lava cools rapidly in the air, dissolved gases expand into bubbles (vesicles) and are trapped as the rock solidifies. Common in Cinder Cones
Uses & applications
Used in high-temperature insulation, drainage rock, gas grill 'lava rocks', landscaping, and as a lightweight aggregate in concrete
Geological facts
Scoria is technically a volcanic glass rather than a crystal. Because of its high surface area and porous nature, it was historically used by Romans as a lightweight building material for domes like the Pantheon
Field identification & locations
Identify by its lightweight feel and numerous visible holes (vesicles). Found near active or extinct volcanic cinder cones in places like Iceland, Hawaii, and the American Southwest
