Scoria (Vesicular Basalt)

Physical Properties

Hardness: 5-6 (Mohs); Color: Dark gray, black, or reddish-brown; Luster: Dull/Submetallic; Texture: Vesicular (pitted with holes); Crystal structure: Aphanitic (microscopic crystals); Specific Gravity: Varries based on porosity, but generally ranges from 2.0 to 3.0.

Formation & Geological History

Formed through the rapid cooling of gas-rich mafic lava. As lava is ejected from a volcano or flows onto the surface, the sudden drop in pressure causes dissolved gases to expand and form bubbles, which are trapped in the rock as it solidifies. Typical of Cenozoic to recent volcanic activity.

Uses & Applications

Commonly used as high-temperature insulation, in landscaping (lava rocks), barbecue grills, as an abrasive in 'stone-washed' jeans manufacture, and as lightweight aggregate in concrete construction.

Geological Facts

Scoria is different from pumice in that it is denser and has larger vesicles with thicker cell walls; while pumice can often float on water, scoria usually sinks. The gas bubbles (vesicles) are often elongated in the direction of the lava flow.

Field Identification & Locations

Identify in the field by its dark color, high porosity (honeycomb appearance), and relatively light weight for its size. Frequently found near volcanic cinder cones like those in the Hawaiian Islands, Iceland, or the Cascades.

Identified on: 4/22/2026

Mode: Standard