igneous
Scoria
Scoriaceous Basalt
Hardness: 5-6 (Mohs). Color: Dark brown, black, or reddish-purplish. Luster: Dull to sub-metallic. Texture: Vesicular (full of holes). Specific Gravity: Approximately 0.8-2.1 (can sometimes float briefly but usually sinks).
- Hardness
- 5-6 (Mohs)
- Color
- Dark brown, black, or reddish-purplish
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 (Mohs). Color: Dark brown, black, or reddish-purplish. Luster: Dull to sub-metallic. Texture: Vesicular (full of holes). Specific Gravity: Approximately 0.8-2.1 (can sometimes float briefly but usually sinks).
Formation & geological history
Formed from gas-rich basaltic or andesitic lava during volcanic eruptions. As the lava is ejected, dissolved gases expand into bubbles (vesicles) which are frozen in place as the rock cools rapidly. Found in volcanic regions like Hawaii, Iceland, and the American West.
Uses & applications
Used in landscaping, gas grills (lava rocks), high-temperature insulation, lightweight concrete aggregate, and traction on icy roads.
Geological facts
Unlike pumice, scoria has thicker vesicle walls and is denser, which is why it usually sinks in water. It is a common constituent of 'cinder cones' found near larger volcanic vents.
Field identification & locations
Identify by its 'swiss cheese' appearance and dark color. It feels rough and abrasive to the touch. Commonly found near the summits of volcanoes or in lava fields.
