igneous
Lava Rock (Scoria)
Extrusive basaltic scoria
Hardness: 5-6 (Mohs scale); Color: Dark reddish-brown to black; Luster: Dull/Earthy; Structure: Highly vesicular (pitted with gas bubbles); Cleavage: None; Specific Gravity: Low (often floats in water temporarily until saturated).
- 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; Structure: Highly vesicular (pitted with gas bubbles); Cleavage: None; Specific Gravity: Low (often floats in water temporarily until saturated).
Formation & geological history
Formed through the rapid cooling of gas-rich basaltic lava erupted from a volcano. The holes (vesicles) are created by gas bubbles that were trapped as the magma solidified. Usually found in Cenozoic volcanic fields.
Uses & applications
Commonly used in landscaping as decorative ground cover, in high-temperature gas grills (lava rocks), as lightweight aggregate in concrete, and for drainage in horticulture.
Geological facts
Scoria is similar to pumice but has larger vesicles and thicker cell walls, making it denser and darker. Because it is formed from basaltic magma, it contains more iron and magnesium than light-colored pumice.
Field identification & locations
Identify in the field by its sponge-like appearance, lightweight feel, and rough, abrasive texture. Commonly found near cinder cones and volcanic vents in places like Arizona, Iceland, and Italy.
