igneous
Scoria (Lava Rock)
Vesicular Basalt / Scoria
Hardness: 5-6 (Mohs); Color: Black to dark reddish-brown; Luster: Dull to submetallic; Structure: Vesicular (highly porous/holey); Specific Gravity: 0.8-2.1 (often floats briefly before sinking).
- Hardness
- 5-6 (Mohs)
- Color
- Black to dark reddish-brown
- Luster
- Dull to submetallic
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Physical properties
Hardness: 5-6 (Mohs); Color: Black to dark reddish-brown; Luster: Dull to submetallic; Structure: Vesicular (highly porous/holey); Specific Gravity: 0.8-2.1 (often floats briefly before sinking).
Formation & geological history
Formed from mafic magma containing abundant dissolved gases during explosive volcanic eruptions. As the lava is ejected, the gases expand and escape, leaving behind rounded voids called vesicles. They represent recent to ancient volcanic activity.
Uses & applications
Used widely in landscaping, gas grills (lava rocks), drainage systems, high-temperature insulation, and as a lightweight aggregate in concrete construction.
Geological facts
Scoria is often confused with pumice, but scoria is heavier, darker, and has larger vesicles with thicker walls. Unlike some pumice, most scoria will not float indefinitely in water.
Field identification & locations
Look for a lightweight, dark, 'spongy' or 'bubbly' texture. It is extremely common in volcanic regions like Hawaii, Iceland, and the Pacific Northwest. Collectors should look for unique shapes or specimens with iridescent coatings.
