igneous
Scoria (Lava Rock)
Vesicular Basalt / Scoria
Hardness: 5-6 (Mohs); Color: Black to dark gray (mafic); Luster: Dull/Earthy; Structure: Vesicular (highly porous/pitted); Specific Gravity: 2.5-3.0 (though it feels lightweight due to air pockets); Cleavage: None.
- Hardness
- 5-6 (Mohs)
- Color
- Black to dark gray (mafic)
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (Mohs); Color: Black to dark gray (mafic); Luster: Dull/Earthy; Structure: Vesicular (highly porous/pitted); Specific Gravity: 2.5-3.0 (though it feels lightweight due to air pockets); Cleavage: None.
Formation & geological history
Formed from the rapid cooling of basaltic or andesitic magma. The holes (vesicles) are created by gas bubbles trapped in the lava as it solidifies at the surface. They range from recent volcanic eruptions to millions of years old.
Uses & applications
Used in landscaping (lava rocks), barbecue grills, high-temperature insulation, lightweight concrete, road construction, and essential oil diffuser jewelry because of its porous nature.
Geological facts
Unlike pumice, which is similar but felsic and often floats, scoria has thicker vesicle walls and a higher density, meaning most specimens will sink in water. It is a classic 'extrusive' igneous rock.
Field identification & locations
Identify in the field by its sponge-like appearance and dark color. It is common in volcanic regions like Hawaii, Iceland, the Canary Islands, and the Western United States. Collectors should look for unique gas bubble patterns.
