igneous
Scoria
Vesicular Mafic Extrusive Igneous Rock
Hardness: 5-6 on the Mohs scale; Color: Black, dark gray, dark brown, or reddish-brown; Luster: Dull; Crystal Structure: Aphanitic with abundant vesicles (gas bubbles); Specific Gravity: Often low due to trapped air, sometimes less than 1.0 (floats on water initially).
- Hardness
- 5-6 on the Mohs scale
- Color
- Black, dark gray, dark brown, or reddish-brown
- Luster
- Dull
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Physical properties
Hardness: 5-6 on the Mohs scale; Color: Black, dark gray, dark brown, or reddish-brown; Luster: Dull; Crystal Structure: Aphanitic with abundant vesicles (gas bubbles); Specific Gravity: Often low due to trapped air, sometimes less than 1.0 (floats on water initially).
Formation & geological history
Formed when gas-rich mafic or intermediate lava erupts from a volcano and cools rapidly, allowing expanding gases to create a spongy, vesicular texture as the rock solidifies.
Uses & applications
Used in lightweight aggregate for concrete, landscaping, barbecue grills (lava rocks), soil conditioning in gardening, and as an abrasive in personal care products like pumice stones.
Geological facts
Scoria is similar to pumice, but it is darker, has larger and more distinct vesicles, and has a higher specific gravity. Unlike pumice, most scoria will eventually sink in water.
Field identification & locations
Easily identified by its dark color, heavy vesicular (holey) structure, and rough texture. Found worldwide near volcanic regions, cinder cones, and basaltic lava flows.
