igneous
Scoria
Vesicular Basalt / Scoria (Mafic volcanic rock)
Hardness: 5-6 (Mohs scale); Color: Dark reddish-brown to black; Luster: Dull/Earthy; Structure: Vesicular (highly porous/holey); Cleavage: None; Specific Gravity: 2.5-3.0 (though it feels light due to air pockets).
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark reddish-brown to black
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark reddish-brown to black; Luster: Dull/Earthy; Structure: Vesicular (highly porous/holey); Cleavage: None; Specific Gravity: 2.5-3.0 (though it feels light due to air pockets).
Formation & geological history
Formed through the rapid cooling of gas-rich mafic magma (lava) ejected from a volcano. The holes, or vesicles, are created by expanding gas bubbles trapped as the lava solidifies. It is usually associated with Cenozoic volcanic activity.
Uses & applications
Commonly used in landscaping (lava rock), gas grill briquettes, high-temperature insulation, drainage stones, and lightweight concrete aggregate. It is rarely used in jewelry due to its abrasive texture.
Geological facts
Scoria is different from pumice because it is mafic (rich in iron and magnesium) and denser; unlike pumice, scoria will usually sink in water. It is a primary component of 'cinder cones' found in volcanic fields.
Field identification & locations
Identify in the field by its distinct 'sponge-like' appearance, rough/sharp edges, and reddish-dark color. It is commonly found in volcanic regions such as the American Southwest, Iceland, and Hawaii.
