igneous
Scoria (Lava Rock)
Scoria
Hardness: 5-6 (Mohs scale); Color: Dark red, reddish-brown, or black; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained) with high vesicularity (pitted with air bubbles); Specific Gravity: 0.8-2.1 (lightweight but usually sinks in water).
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark red, reddish-brown, or black
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark red, reddish-brown, or black; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained) with high vesicularity (pitted with air bubbles); Specific Gravity: 0.8-2.1 (lightweight but usually sinks in water).
Formation & geological history
Formed from mafic (basaltic) magma ejected from volcanoes. As the lava cools rapidly at the surface, gases dissolved in the magma expand and create bubbles (vesicles) that become frozen in the rock. It is typically found in volcanic cones and cinder cones.
Uses & applications
Used widely in landscaping, gas grills (lava rocks), drainage systems, high-temperature insulation, and as a lightweight aggregate in concrete/cinder blocks.
Geological facts
Scoria is different from pumice in that it contains larger vesicles and thicker cell walls, making it denser. If a volcanic rock floats on water, it is pumice; if it sinks, it is typically scoria.
Field identification & locations
Identify in the field by its distinct vesicular (bubbly) texture, lightweight feel relative to size, and dark red or black color. Common in volcanic regions such as the American Southwest, Iceland, and Italy.
