Scoria (Vesicular Basalt)

Physical Properties

Hardness: 5-6 Mohs. Color: Reddish brown to dark grey/black. Luster: Dull/Earthy. Structure: Highly vesicular (pitted with gas bubbles). Specific gravity: Low (often floats briefly/feels light).

Formation & Geological History

Formed from gas-rich basaltic magma cooling rapidly near the surface of a volcano. The gas bubbles (vesicles) are trapped as the lava solidifies. Typically associated with Cenozoic volcanic activity.

Uses & Applications

Used in landscaping (lava rocks), high-temperature insulation, drainage stones, gas grills, and as a lightweight aggregate in concrete.

Geological Facts

Scoria is different from pumice because it has thicker cell walls and is denser, causing it to sink in water eventually, whereas pumice often floats indefinitely.

Field Identification & Locations

Identify by its 'Swiss cheese' appearance, lightweight feel, and rough, abrasive texture. Commonly found near cinder cones and basaltic lava flows in volcanic regions like the American Southwest, Iceland, or Italy.

Identified on: 4/22/2026

Mode: Standard