Scoria

Physical Properties

Mohs Hardness: 5-6, Color: Reddish-brown to black, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained matrix), Texture: Highly vesicular (pitted with gas bubbles), Density: Low (often floats briefly on water).

Formation & Geological History

Formed from the rapid cooling of gas-rich basaltic or andesitic magma during volcanic eruptions. The cooling trapped gas bubbles, creating the pitted texture. Typically formed in the Cenozoic era in volcanic fields.

Uses & Applications

Used in landscaping, gas grill lava rocks, high-temperature insulation, lightweight aggregate in concrete, and traction on icy roads.

Geological Facts

Scoria is often confused with pumice, but it is denser and has larger vesicles with thicker walls. Many of the famous Moai statues on Easter Island wear hats (pukao) carved from red scoria.

Field Identification & Locations

Identify by its 'Swiss cheese' appearance, lightweight feel, and rough, abrasive texture. Commonly found in volcanic regions like the Cascades, Iceland, and the Canary Islands.

Identified on: 5/16/2026

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