igneous
Scoria
Scoria (Vesicular Basalt)
Hardness: 5-6 Mohs; Color: Dark red, brownish-black, or charcoal; Luster: Dull to earthy; Structure: Highly vesicular (honeycombed with gas bubbles); Specific Gravity: 2.0-3.0 (heavy enough to sink in water, unlike pumice)
- Hardness
- 5-6 Mohs
- Color
- Dark red, brownish-black, or charcoal
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-6 Mohs; Color: Dark red, brownish-black, or charcoal; Luster: Dull to earthy; Structure: Highly vesicular (honeycombed with gas bubbles); Specific Gravity: 2.0-3.0 (heavy enough to sink in water, unlike pumice)
Formation & geological history
Formed from the rapid cooling of mafic magma (rich in iron and magnesium) during volcanic eruptions. As the lava is ejected, dissolved gases expand and escape, creating the characteristic bubble-like cavities (vesicles). It is typically found in volcanic cinder cones.
Uses & applications
Used extensively in landscaping and decorative gardening, gas grill lava rocks, high-temperature insulation, and as lightweight aggregate in concrete or drainage systems.
Geological facts
Scoria differs from pumice because it has thicker cell walls and larger vesicles; while pumice floats, scoria almost always sinks. It was historically used in the construction of the Pantheon in Rome to reduce the weight of the dome.
Field identification & locations
Identify in the field by its dark color, bubbly texture (vesicles), and rough, sharp edges. It is much heavier than floating pumice and is commonly found on the slopes of volcanoes or in volcanic fields like those in Arizona, Hawaii, or Iceland.
