igneous
Scoria
Extrusive Mafic Volcanic Rock
Hardness: 5-6 Mohs. Color: usually dark-colored (black, charcoal, or dark brown). Luster: dull to submetallic. Crystal structure: vesicular and aphanitic (fine-grained). Specific gravity: very low (sometimes floats initially due to air pockets).
- Hardness
- 5-6 Mohs
- Color
- usually dark-colored (black, charcoal, or dark brown)
- Luster
- dull to submetallic
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Physical properties
Hardness: 5-6 Mohs. Color: usually dark-colored (black, charcoal, or dark brown). Luster: dull to submetallic. Crystal structure: vesicular and aphanitic (fine-grained). Specific gravity: very low (sometimes floats initially due to air pockets).
Formation & geological history
Formed from gas-rich, frothy basaltic magma that cools rapidly during volcanic eruptions. The escaping gases create the characteristic pitted or vesicular texture.
Uses & applications
Commonly used in landscaping (lava rocks), BBQ grills as heat conductors, lightweight concrete, high-temperature insulation, and trail surfacing.
Geological facts
Scoria is different from pumice because its vesicles are larger and it has thicker cell walls, making it dense enough to usually sink in water, whereas pumice often floats.
Field identification & locations
Identify in the field by its dark color, sandpaper-like texture (very rough), and numerous small holes (vesicles). Found predominantly in volcanic regions like Hawaii, the Cascades, or Italy.
