igneous
Scoria (Lava Rock)
Mafic Volcanic Scoria
Hardness: 5-6 Mohs. Color: Black, dark gray, or reddish-brown (due to oxidation). Luster: Dull to sub-metallic. Structure: Vesicular (highly porous/holey). Specific Gravity: Approximately 0.8 to 2.1 (often floats briefly then sinks).
- Hardness
- 5-6 Mohs
- Color
- Black, dark gray, or reddish-brown (due to oxidation)
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs. Color: Black, dark gray, or reddish-brown (due to oxidation). Luster: Dull to sub-metallic. Structure: Vesicular (highly porous/holey). Specific Gravity: Approximately 0.8 to 2.1 (often floats briefly then sinks).
Formation & geological history
Formed from the rapid cooling of mafic lava rich in volatiles (gases) during explosive volcanic eruptions. As the lava cools instantly, expanding gas bubbles are trapped, creating the hole-filled texture. Found in volcanic fields of various ages, from Cenozoic to modern.
Uses & applications
Used extensively in landscaping, gas grills (lava rocks), high-temperature insulation, lightweight concrete aggregate, and road traction on icy surfaces.
Geological facts
Scoria differs from pumice in that it has larger vesicles and thicker cell walls, making it denser and darker. Red scoria, like that seen on the bottom of the specimen, gets its hue from the oxidation of iron within the lava while it is still hot.
Field identification & locations
Identify by its dark color, light weight compared to solid rock, and 'Swiss cheese' texture. Commonly found near cinder cones or volcanic vents in places like Iceland, Italy, the Canary Islands, and the Western United States.
