igneous
Lava Rock (Scoria)
Scoria (Vesicular Basalt)
Hardness: 5-6 Mohs. Color: Dark brown, black, or reddish-brown. Luster: Dull/earthy to sub-metallic. Crystal structure: Aphanitic (fine-grained) with many vesicles (holes). Specific gravity: 0.8–2.1 (relatively low due to air pockets).
- Hardness
- 5-6 Mohs
- Color
- Dark brown, black, or reddish-brown
- Luster
- Dull/earthy to sub-metallic
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Physical properties
Hardness: 5-6 Mohs. Color: Dark brown, black, or reddish-brown. Luster: Dull/earthy to sub-metallic. Crystal structure: Aphanitic (fine-grained) with many vesicles (holes). Specific gravity: 0.8–2.1 (relatively low due to air pockets).
Formation & geological history
Formed from the rapid cooling of gas-rich mafic magma (basaltic) extruded from a volcano. The gas bubbles are trapped as the lava solidifies, creating the 'vesicular' texture. Most common in recent Quaternary volcanic fields but found throughout geological history.
Uses & applications
Extensively used in landscaping (lava rock), high-temperature insulation, concrete aggregate, gas grills, and drainage systems. Occasionally used for aquarium decor and stone-washing textiles like jeans.
Geological facts
Scoria is often confused with pumice, but scoria is denser, has larger vesicles, and generally sinks in water, whereas pumice floats. It is a major component of cinder cones around the world.
Field identification & locations
Identify in the field by its very high porosity, dark color, and sharp, abrasive surface. Common in volcanic regions like Hawaii, Iceland, and the American Southwest. Collectors should look for unique aerodynamic shapes (volcanic bombs) or interesting color variations.
