igneous
Scoria
Highly vesicular mafic volcanic rock
Hardness: 5-6 (Mohs scale); Color: Dark brown, black, or reddish; Luster: Dull (sub-vitreous); Crystal Structure: Aphanitic (fine-grained) with many vesicles; Specific Gravity: 2.0-3.0 (though it often feels light due to air pockets).
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark brown, black, or reddish
- Luster
- Dull (sub-vitreous)
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark brown, black, or reddish; Luster: Dull (sub-vitreous); Crystal Structure: Aphanitic (fine-grained) with many vesicles; Specific Gravity: 2.0-3.0 (though it often feels light due to air pockets).
Formation & geological history
Formed from the explosive eruption of basaltic or andesitic lava. As the gas-rich lava is ejected, the pressure drops and gases expand to create bubbles (vesicles) before the rock solidifies. Common in volcanic cones like cinder cones.
Uses & applications
Used widely in landscaping, gas grill heat stones, high-temperature insulation, drainage rock, and as an abrasive in stone-washing textiles.
Geological facts
Unlike pumice, scoria has a higher density and thicker vesicle walls, which prevents most scoria specimens from floating in water. Many of the 'lava rocks' found in backyard barbecues and landscapes are actually scoria.
Field identification & locations
Identify by its dark color, rough/bubbly texture, and being relatively light for its size but heavier than pumice. Common in volcanic regions such as Iceland, Hawaii, and the Canary Islands.
