igneous
Scoria (Lava Rock)
Vesicular Basalt / Scoria
Hardness: 5-6 (Mohs scale); Color: Dark grey, black, or reddish-brown; Luster: Dull/earthy; Crystal structure: Aphanitic (microcrystalline); Cleavage: None; Specific gravity: Low due to vesicles (holes).
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark grey, black, or reddish-brown
- Luster
- Dull/earthy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark grey, black, or reddish-brown; Luster: Dull/earthy; Crystal structure: Aphanitic (microcrystalline); Cleavage: None; Specific gravity: Low due to vesicles (holes).
Formation & geological history
Formed from gas-rich mafic magma (basaltic or andesitic) that cools rapidly at the surface during volcanic eruptions. The holes (vesicles) are created by trapped gas bubbles that expand as pressure drops during the eruption.
Uses & applications
Commonly used in landscaping as decorative 'lava rock,' in gas grills to distribute heat, as a lightweight aggregate in concrete/cinder blocks, and for high-temperature insulation.
Geological facts
Scoria differs from pumice in that it has larger vesicles and thicker cell walls, making it dense enough to sink in water, whereas pumice usually floats.
Field identification & locations
Identify in the field by its sponge-like or honeycombed appearance, dark color, and sharp, jagged edges. Common in areas of recent volcanic activity like Hawaii, Iceland, and the American Southwest.
