igneous
Scoria
Vesicular Basalt / Scoria
Hardness: 5-6 (Mohs scale); Color: Dark brown, black, or reddish-purple; Luster: Dull/Earthy; Structure: Highly vesicular (pitted with holes); Specific Gravity: 0.8-2.1 (relatively light but usually sinks in water, unlike pumice); Cleavage: None.
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark brown, black, or reddish-purple
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark brown, black, or reddish-purple; Luster: Dull/Earthy; Structure: Highly vesicular (pitted with holes); Specific Gravity: 0.8-2.1 (relatively light but usually sinks in water, unlike pumice); Cleavage: None.
Formation & geological history
Formed from basaltic or andesitic magma. As the magma erupts from a volcano, dissolved gases create bubbles that are trapped as the rock cools rapidly. It is typically associated with cinder cones and shield volcanoes from the Cenozoic era to the present.
Uses & applications
Used in landscaping (drainage and decoration), high-temperature insulation, lightweight concrete, gas grill briquettes, and road traction on snowy surfaces.
Geological facts
Scoria is often confused with pumice, but scoria has larger vesicles, thicker cell walls, and is denser. While pumice floats, scoria usually sinks in water.
Field identification & locations
Identify by its dark color and 'sponge-like' appearance with numerous visible pits (vesicles). It is commonly found in volcanic regions like Hawaii, the Pacific Northwest of the USA, Iceland, and Italy.
