Scoria (Lava Rock)

Physical Properties

Hardness: 5-6 (Mohs scale); Color: Dark reddish-brown to black; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained) with high vesicularity (pitted texture); Specific Gravity: 0.8-2.1 (lightweight and often floats on water briefly).

Formation & Geological History

Formed from extrusive volcanic activity. As gas-rich basaltic or andesitic magma is ejected from a volcano, the rapid cooling and depressurization trap gas bubbles (vesicles) within the rock as it solidifies.

Uses & Applications

Commonly used in landscaping (decorative rock), high-temperature insulation, gas grills (lava rocks), drainage systems, and as a lightweight aggregate in concrete.

Geological Facts

Scoria is often mistaken for pumice; however, scoria has larger vesicles and thicker cell walls, making it denser and darker than pumice. It is the primary component of many volcanic cinder cones.

Field Identification & Locations

Identify by its 'sponge-like' or 'honeycomb' appearance, lightweight feel, and sharp, abrasive edges. Commonly found in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.

Identified on: 4/26/2026

Mode: Standard