igneous
Scoria (Lava Rock)
Scoria (Mafic volcanic rock)
Hardness: 5-6 (variable); Color: Black, dark gray, or reddish-brown; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained) with high vesicularity (holes); Specific Gravity: Low (often floats initially until water-logged).
- Hardness
- 5-6 (variable)
- Color
- Black, dark gray, or reddish-brown
- Luster
- Dull/earthy
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Physical properties
Hardness: 5-6 (variable); Color: Black, dark gray, or reddish-brown; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained) with high vesicularity (holes); Specific Gravity: Low (often floats initially until water-logged).
Formation & geological history
Formed from the rapid cooling of gas-rich mafic magma (basaltic or andesitic) during explosive volcanic eruptions. The holes (vesicles) are formed by trapped gas bubbles.
Uses & applications
Commonly used in landscaping, gas barbecue grills, high-temperature insulation, drainage rock, and as an abrasive in stone-washed denim.
Geological facts
Scoria is often confused with pumice, but scoria is denser, has larger vesicles, and is darker in color due to its higher iron and magnesium content.
Field identification & locations
Identify by its 'sponge-like' appearance, dark color, and lightweight feel despite being solid rock. Commonly found near cinder cones and volcanic vents.
