igneous
Scoria (Lava Rock)
Scoria (Mafic Volcanic Rock)
Hardness: 5-6 (Mohs); Color: Dark reddish-brown to black; Luster: Dull (earthy); Crystal structure: Aphanitic/fragmental (microscopic crystals); Cleavage: None; Specific gravity: 0.8-2.0 (often floats on water briefly before absorbing it); Texture: Highly vesicular with large, distinct pores.
- Hardness
- 5-6 (Mohs)
- Color
- Dark reddish-brown to black
- Luster
- Dull (earthy)
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark reddish-brown to black; Luster: Dull (earthy); Crystal structure: Aphanitic/fragmental (microscopic crystals); Cleavage: None; Specific gravity: 0.8-2.0 (often floats on water briefly before absorbing it); Texture: Highly vesicular with large, distinct pores.
Formation & geological history
Formed from the cooling of gas-rich mafic magma (basaltic or andesitic) ejected from a volcano. The gas bubbles are trapped as the lava solidifies rapidly. Usually found in cinder cones and volcanic vents, ranging from recent Holocene deposits to millions of years old.
Uses & applications
Commonly used in landscaping (lava rock), high-temperature insulation, drainage stones, gas grills (to distribute heat), and as a lightweight aggregate in concrete construction.
Geological facts
Scoria is often confused with pumice; however, scoria has thicker vesicle walls and is denser, causing it to sink in water, whereas pumice typically floats. The red color is usually due to the oxidation of iron within the lava at the time of eruption.
Field identification & locations
Identify in the field by its sponge-like texture, sharp edges, and light weight compared to solid basalt. It is commonly found in volcanic regions like Iceland, Hawaii, the Canary Islands, and the Cinder Cone Natural Landmark in California.
