igneous
Scoria (Vesicular Basalt)
Scoria (Extrusive Igneous Rock)
Hardness: 5-6 (Mohs scale), Color: Dark red, reddish-brown, or black (oxidized in this specimen), Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained) with high vesicularity (pitted with gas bubbles), Specific Gravity: 0.8 to 2.1 (often floats on water briefly but usually sinks).
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Physical properties
Hardness: 5-6 (Mohs scale), Color: Dark red, reddish-brown, or black (oxidized in this specimen), Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained) with high vesicularity (pitted with gas bubbles), Specific Gravity: 0.8 to 2.1 (often floats on water briefly but usually sinks).
Formation & geological history
Formed from cinder cone volcanic eruptions where gas is trapped in cooling lava. The reddish color indicates the oxidation of iron-rich minerals (magnetite or olivine) within the basaltic magma as it cooled in an oxygen-rich environment.
Uses & applications
Used in landscaping (lava rock), gas grill briquettes, high-temperature insulation, drainage stones, and lightweight concrete aggregate.
Geological facts
Scoria is often mistaken for pumice, but scoria has larger vesicles, thicker walls, and is denser. The deep red color is a result of iron rusting inside the rock during or after the eruption.
Field identification & locations
Identify in the field by its very lightweight, 'sponge-like' appearance and numerous holes (vesicles). It is commonly found around volcanic vents and cinder cones, such as those in the Western United States or Iceland.
