Igneous
Scoria (Lava Rock)
Scoria (Basaltic Scoria)
Hardness: 5-6 (Mohs scale); Color: Dark brown, black, or reddish-purplish; Luster: Dull (earthy); Crystal Structure: Aphanitic (fine-grained) with vesicular texture (holed); Specific Gravity: 2.0-3.0 (often low enough to feel light but dense enough to sink in water).
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark brown, black, or reddish-purplish
- Luster
- Dull (earthy)
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark brown, black, or reddish-purplish; Luster: Dull (earthy); Crystal Structure: Aphanitic (fine-grained) with vesicular texture (holed); Specific Gravity: 2.0-3.0 (often low enough to feel light but dense enough to sink in water).
Formation & geological history
Formed from basaltic or andesitic magma expelled from a volcano as gas-rich froth. It cools quickly while gases are still escaping, creating the 'vesicles' or holes. It can be found in any age range associated with volcanic activity, from modern eruptions to millions of years old.
Uses & applications
Commonly used in landscaping (lava rocks), high-temperature insulation, drainage rock, gas grill briquettes, and as a lightweight aggregate in concrete.
Geological facts
Unlike pumice, which is also vesicular, scoria usually has thicker vesicle walls and is denser, meaning it will sink in water while pumice floats. It is often found on the flanks of cinder cone volcanoes.
Field identification & locations
Identify by its 'sponge-like' appearance, dark color, and rough, abrasive texture. Commonly found in volcanic regions like Iceland, Hawaii, Italy, and the Western United States. Collectors should look for unique gas bubble patterns or 'lava bombs' containing crystals like olivine.
