igneous
Lava Rock (Scoria)
Scoria (highly vesicular basaltic rock)
Hardness: 5-6 (Mohs scale); Color: Dark reddish-brown to black; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained) with high vesicularity (pitted surface); Cleavage: None; Specific gravity: 2.5-3.0 (though it often feels lighter due to air pockets).
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark reddish-brown to black
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark reddish-brown to black; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained) with high vesicularity (pitted surface); Cleavage: None; Specific gravity: 2.5-3.0 (though it often feels lighter due to air pockets).
Formation & geological history
Formed from the cooling of gas-rich basaltic lava. During a volcanic eruption, gases trapped in the magma expand rapidly as pressure is released, creating a frothy texture that solidifies into a stone with many small holes (vesicles).
Uses & applications
Commonly used in landscaping (ground cover), high-temperature insulation, oil well drilling, gas grills (lava rocks), and sometimes as a lightweight aggregate in concrete construction.
Geological facts
Scoria differs from pumice because it has larger vesicles and thicker cell walls, making it dense enough to sink in water, whereas pumice typically floats. It is often harvested from cinder cones.
Field identification & locations
Identify in the field by its dark color, rough/scratchy texture, and abundance of small holes. It is commonly found in volcanic regions such as the Western United States, Iceland, and Italy. Collectors look for unique shapes or oxidation colors.
