igneous
Red Scoria
Scoria (Vesicular Basalt/Andesite)
Hardness: 5-6 Mohs. Color: Reddish-brown to dark red (due to iron oxidation). Luster: Dull to sub-vitreous. Structure: Highly vesicular (porous). Cleavage: None. Specific gravity: Variable but low (often sinks in water, unlike pumice).
- Hardness
- 5-6 Mohs
- Color
- Reddish-brown to dark red (due to iron oxidation)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5-6 Mohs. Color: Reddish-brown to dark red (due to iron oxidation). Luster: Dull to sub-vitreous. Structure: Highly vesicular (porous). Cleavage: None. Specific gravity: Variable but low (often sinks in water, unlike pumice).
Formation & geological history
Formed from gas-rich magma (mafic to intermediate) ejected during explosive volcanic eruptions. As the lava cools rapidly, the gases expand and escape, leaving behind a frozen 'foam' of bubbles or vesicles. Formed during the Cenozoic era in recent volcanic fields.
Uses & applications
Commonly used in landscaping (decorative 'lava rock'), gas grill bases for heat retention, high-temperature insulation, drainage rock, and in lightweight concrete as aggregate.
Geological facts
Scoria is often confused with pumice, but it is denser and has thicker vesicle walls. It is a key component of volcanic cones called 'cinder cones'. The red color is caused by the oxidation of iron-bearing minerals during or shortly after the eruption.
Field identification & locations
Identify in the field by its sponge-like appearance and light weight compared to solid rock. It is found in volcanic regions such as the American Southwest, Iceland, and Hawaii. It feels rough and abrasive to the touch.
