Scoria (Lava Rock)

Physical Properties

Hardness: 5-6 (Mohs scale); Color: Dark brown, black, or reddish-purple; Luster: Dull/earthy; Crystal structure: Aphanitic (fine-grained) with large vesicules; Specific gravity: Low (often floats briefly/lightweight).

Formation & Geological History

Formed from gas-rich basaltic or andesitic magma. As the magma erupts, gases expand quickly and are trapped as the lava cools rapidly, creating a 'frothy' vesicular texture.

Uses & Applications

Used in landscaping (lava rock), high-temperature insulation, gas grills, lightweight concrete aggregate, and decorative garden mulch.

Geological Facts

Scoria differs from pumice because it has thicker cell walls and a higher density, which usually causes it to sink in water, whereas pumice often floats. It is often used as a natural abrasive.

Field Identification & Locations

Identify by its highly vesicular (bubbly) texture, dark color, and light weight relative to appearance. Commonly found near cinder cones and volcanic vents in regions like Iceland, Italy, or the western USA.

Identified on: 4/20/2026

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