igneous
Scoria
Scoria (Vesicular Basalt/Andesite)
Hardness: 5-6 (Mohs scale); Color: Dark reddish-brown to black; Luster: Dull/Earthy; Structure: Vesicular (highly porous/holed); Texture: Aphanitic (fine-grained) with large gas bubbles.
- 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: Vesicular (highly porous/holed); Texture: Aphanitic (fine-grained) with large gas bubbles.
Formation & geological history
Formed from the rapid cooling of gas-rich mafic lava during volcanic eruptions. The holes (vesicles) are created by gas bubbles trapped in the molten rock as it solidifies. Commonly found near cinder cones and strato-volcanoes.
Uses & applications
Used extensively in landscaping, gas grill lava rocks, lightweight concrete aggregate, high-temperature insulation, and as a drainage material in horticulture.
Geological facts
Scoria is often confused with pumice, but scoria is denser and usually sinks in water, whereas pumice often floats. The holes are technically called vesicles. It is a key component of volcanic cinder cones.
Field identification & locations
Identify in the field by its sponge-like appearance, lightweight feel (though heavier than pumice), and sharp, abrasive edges. Common in volcanic regions like Hawaii, the Andes, and the Western United States.
