igneous
Scoria (with Iron Oxidation)
Vesicular Basalt / Scoria
Hardness: 5-6 Mohs. Color: Black to dark gray base with reddish-brown to orange oxidation. Luster: Dull to sub-metallic. Structure: Highly vesicular (honeycombed). Specific Gravity: 2.5-3.0 (though it feels light due to air pockets).
- Hardness
- 5-6 Mohs
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs. Color: Black to dark gray base with reddish-brown to orange oxidation. Luster: Dull to sub-metallic. Structure: Highly vesicular (honeycombed). Specific Gravity: 2.5-3.0 (though it feels light due to air pockets).
Formation & geological history
Formed from the rapid cooling of gas-rich mafic magma (lava) ejected during explosive volcanic eruptions. The holes (vesicles) are created by trapped gas bubbles. Common in Cenozoic volcanic fields.
Uses & applications
Used extensively in landscaping, gas grill lava rocks, high-temperature insulation, lightweight concrete aggregate, and as a traction aid on icy roads.
Geological facts
Red scoria gets its color from the oxidation of iron-rich minerals (like olivine or pyroxene) while the rock is still hot or through subsequent weathering, turning magnetite/ilmenite into hematite or limonite.
Field identification & locations
Identify by its 'sponge-like' appearance and dark color. Unlike pumice, scoria typically sinks in water. Found near cinder cones and volcanic vents in regions like Iceland, Hawaii, and the Western United States.
