igneous
Scoria (Lava Rock)
Scoria (extrusive volcanic rock)
Hardness: 5-6 Mohs scale; Color: Dark red, black, or dark brown; Luster: Dull/Earthy; Crystal Structure: Amorphous/Vesicular; Cleavage: None; Specific Gravity: Low (often floats briefly on water)
- Hardness
- 5-6 Mohs scale
- Color
- Dark red, black, or dark brown
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 Mohs scale; Color: Dark red, black, or dark brown; Luster: Dull/Earthy; Crystal Structure: Amorphous/Vesicular; Cleavage: None; Specific Gravity: Low (often floats briefly on water)
Formation & geological history
Formed from gas-rich basaltic or andesitic magma. As the magma erupts and cools rapidly at the surface, trapped gas bubbles form small, rounded cavities called vesicles.
Uses & applications
Used in landscaping, gas grills (lava rocks), drainage systems, high-temperature insulation, and as a lightweight aggregate in concrete.
Geological facts
Scoria differs from pumice because it has larger vesicles and thicker cell walls, making it dense enough to usually sink in water, whereas pumice often floats. It is a major component of cinder cones.
Field identification & locations
Identify by its highly vesicular (bubbly) texture, lightweight feel, and rough, abrasive surface. Commonly found near active or dormant volcanic cinder cones in places like Hawaii, Iceland, and the American Southwest.
