Igneous
Scoria (Lava Rock)
Scoria (Vesicular Basaltic Rock)
Hardness: 5-6 (Mohs scale); Color: Dark reddish-brown to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) with large vesicles (gas pockets); Cleavage: None; Specific Gravity: Low (often floats in water initially but sinks once saturated).
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark reddish-brown to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark reddish-brown to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) with large vesicles (gas pockets); Cleavage: None; Specific Gravity: Low (often floats in water initially but sinks once saturated).
Formation & geological history
Formed from the rapid cooling of basaltic or andesitic lava containing high concentrations of dissolved gases. As the pressure drops during an eruption, the gases expand and create bubbles (vesicles) that are trapped as the lava solidifies. Found primarily in volcanic cinder cones and flow surfaces.
Uses & applications
Used widely in landscaping (lava rock), gas grills for heat retention, lightweight concrete aggregate, high-temperature insulation, and as an abrasive in stone-washing textiles.
Geological facts
Scoria is the primary component of cinder cones, which are the most common type of volcano. Unlike pumice, which is also vesicular, scoria is denser and usually dark-colored due to its higher iron and magnesium content.
Field identification & locations
Identify in the field by its sponge-like or honeycomb appearance, rough/sharp edges, and reddish-brown to black color. Common in volcanic regions such as Hawaii, Iceland, and the American Southwest. Collectors should look for intact vesicles and iridescent coatings.
