igneous
Vesicular basalt (likely iron-rich volcanic scoria)
Basalt; predominantly plagioclase, clinopyroxene, olivine, and iron oxides
AI-generated identification · may be incorrectHardness about 5–6 Mohs; dark gray to brown-black, locally reddish from oxidation, with dull to submetallic luster and abundant rounded vesicles. Fine-grained, massive, and non-cleavable; the pale fillings may be secondary zeolite, calcite, or silica minerals.
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Physical properties
Hardness about 5–6 Mohs; dark gray to brown-black, locally reddish from oxidation, with dull to submetallic luster and abundant rounded vesicles. Fine-grained, massive, and non-cleavable; the pale fillings may be secondary zeolite, calcite, or silica minerals.
Formation & geological history
Formed when mafic lava cooled rapidly at or near Earth’s surface, with trapped gas producing vesicles; oxidation created the reddish-brown surfaces. Basalt ranges from recent volcanic eruptions to rocks billions of years old, but this specimen’s age cannot be determined visually.
Uses & applications
Used widely as crushed aggregate, road stone, riprap, railway ballast, and decorative stone; attractive vesicular pieces are collected or used in landscaping. Usually low commercial value unless the cavities contain collectible minerals.
Geological facts
The rounded cavities are gas bubbles rather than fossils. Metallic-looking specks and coatings commonly represent magnetite, hematite, or weathered sulfides.
Field identification & locations
Identify by its black, fine-grained volcanic texture, vesicles, and relatively high density; a magnet may attract it weakly to strongly if magnetite-rich. Common worldwide in volcanic regions, including Hawaii, Iceland, India, and oceanic crust.
