Basalt Scoria

Physical Properties

Hardness: 5-6 Mohs; Color: black to dark brown; Luster: dull to earthy; Texture: highly vesicular (pitted with gas bubbles); Crystal Structure: fine-grained (aphanitic) or glassy

Formation & Geological History

Formed from the rapid cooling of basaltic lava containing dissolved gases. As the lava erupts, the gases expand and form bubbles (vesicles) that are trapped as the rock solidifies. Common in Cenozoic volcanic fields.

Uses & Applications

Used in landscaping, high-temperature insulation, drainage rock, and as an abrasive. In construction, it is used for lightweight concrete and road base.

Geological Facts

Scoria is often confused with pumice, but it is denser and darker. Because it is basaltic, it contains more iron and magnesium than the lighter-colored pumice.

Field Identification & Locations

Identified in the field by its dark color, heavy weight relative to its appearance (though light for a rock), and numerous open cavities. Commonly found near cinder cones and volcanic vents.

Identified on: 5/7/2026

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