igneous
Scoria
Vesicular Mafic Igneous Rock
Hardness on Mohs scale is typically 5 to 6; color ranges from black or dark gray to dark reddish-brown; luster is dull; crystal structure is aphanitic (fine-grained) with abundant vesicles (air bubbles); specific gravity is less than 1.0 for some pieces, allowing them to float, though most are dense enough to sink.
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Physical properties
Hardness on Mohs scale is typically 5 to 6; color ranges from black or dark gray to dark reddish-brown; luster is dull; crystal structure is aphanitic (fine-grained) with abundant vesicles (air bubbles); specific gravity is less than 1.0 for some pieces, allowing them to float, though most are dense enough to sink.
Formation & geological history
Formed when gas-rich mafic or intermediate lava erupts from a volcano or effuses from a vent, cooling rapidly enough to trap gas bubbles inside the solidifying rock.
Uses & applications
Used extensively in lightweight aggregate for concrete, landscaping ground cover, barbecue grill stones, drainage systems, and as an abrasive in personal care products.
Geological facts
Scoria is often confused with pumice, but scoria is darker, denser, and has larger, more distinct vesicles with thicker walls, and typically sinks in water.
Field identification & locations
Easily identified by its dark color, rough texture, and numerous gas cavities (vesicular texture). Common near volcanic regions worldwide, including volcanic fields in the western United States, Italy, and Iceland.
