igneous

Limonitic Scoria (Vesicular Basalt with Iron Staining)

Highly vesicular basalt heavily stained by Limonite [FeO(OH)·nH2O]

Hardness: 5-6 (Mohs scale); Color: Yellowish-brown to rusty orange due to iron oxidation over a dark grey base; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained) with high vesicularity (pitted texture); Cleavage: None/Conchoidal.

Hardness: 5-6 (Mohs scale)
Luster: Dull/Earthy

Identified March 14, 2026More igneous →

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Physical properties

Formation & geological history

Formed from extrusive volcanic activity where gas bubbles were trapped in cooling lava (making it 'vesicular'). The yellow-orange color is a secondary process where iron-rich minerals in the basalt weathered into Limonite through exposure to oxygen and water over decades to centuries. Geologically common from the Cenozoic era to recent volcanic events.

Uses & applications

Common varieties are used in landscaping, gas grill heat dispersion, high-temperature insulation, and as a lightweight aggregate in concrete construction.

Geological facts

Scoria is so porous that its density is significantly lower than solid basalt, though unlike pumice, it usually does not float in water. The rusty 'ochre' color was often used by ancient cultures as a natural pigment for cave paintings and pottery.

Field identification & locations

Identify in the field by its 'Swiss cheese' texture and light weight relative to appearance. It is commonly found in volcanic fields, cinder cones, and near basaltic lava flows in regions like the Pacific Northwest, Iceland, and Hawaii.

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