igneous
Scoria (Vesicular Basalt)
Scoria
Hardness: 5-6 (Mohs scale); Color: Reddish-brown to dark gray; Luster: Dull/Earthy; Structure: Vesicular (highly porous/holey); Specific Gravity: Relatively low because of air pockets, though denser than pumice.
- Hardness
- 5-6 (Mohs scale)
- Color
- Reddish-brown to dark gray
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Reddish-brown to dark gray; Luster: Dull/Earthy; Structure: Vesicular (highly porous/holey); Specific Gravity: Relatively low because of air pockets, though denser than pumice.
Formation & geological history
Formed through the rapid cooling of basaltic or andesitic lava with high gas content. As the lava erupts, gas bubbles are trapped, creating the vesicular texture. It is typical of volcanic cinder cones and can range in age from very recent to millions of years old.
Uses & applications
Used widely in landscaping (lava rock), construction for lightweight aggregate in concrete, as insulation, and in high-temperature gas grills. It is also used as a decorative stone in aquariums.
Geological facts
Scoria differs from pumice because it has larger vesicles and thicker cell walls, making it denser; unlike pumice, most scoria will sink in water. It is the primary component of many cinder cone volcanoes like those found in the American Southwest.
Field identification & locations
Identify in the field by its dark red/black color and sponge-like appearance with visible holes. It is commonly found near volcanic vents in regions like Hawaii, Iceland, and the Cascade Range. Collectors look for pieces with unique colors or larger, intact vesicles.
