igneous
Basaltic Scoria
Scoria (Vesicular Basalt/Andesite)
Hardness: 5-6 (Mohs scale), Color: Dark brown, black, or reddish-brown (due to iron oxidation), Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), highly vesicular with many gas bubbles/holes, Specific Gravity: Low (often floats briefly/feels light).
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Physical properties
Hardness: 5-6 (Mohs scale), Color: Dark brown, black, or reddish-brown (due to iron oxidation), Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), highly vesicular with many gas bubbles/holes, Specific Gravity: Low (often floats briefly/feels light).
Formation & geological history
Formed from volcanic eruptions where gas-rich lava is ejected and cools rapidly. The trapped gases expand to create a frothy, hole-filled texture. These can originate from Cenozoic to recent volcanic activity.
Uses & applications
Used extensively in landscaping (lava rocks), gas grill heating stones, high-temperature insulation, and as a lightweight aggregate in concrete or for traction on icy roads.
Geological facts
Scoria is different from pumice because it has thicker cell walls and is denser, which usually prevents it from floating in water for long periods. The red color seen in many specimens is caused by the oxidation of iron within the lava as the scoria forms.
Field identification & locations
Identify in the field by its sponge-like, porous appearance and dark/reddish coloration. It is commonly found near volcanic cones (cinder cones) in places like Iceland, Hawaii, and the Western United States (Arizonia, New Mexico).
