igneous
Blue-gray basalt (likely vesicular basalt)
Basalt; primarily plagioclase feldspar, clinopyroxene, and often olivine or iron oxides
AI-generated identification · may be incorrectFine-grained, dark blue-gray rock with scattered pale mineral patches and possible small vesicles; typically Mohs 5–6, dull to slightly vitreous luster, massive texture, and no obvious cleavage. Specific gravity is about 2.8–3.0.
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Physical properties
Fine-grained, dark blue-gray rock with scattered pale mineral patches and possible small vesicles; typically Mohs 5–6, dull to slightly vitreous luster, massive texture, and no obvious cleavage. Specific gravity is about 2.8–3.0.
Formation & geological history
An extrusive igneous rock formed when mafic lava rapidly cooled at or near Earth’s surface, commonly during Cenozoic or older volcanic activity. The pale areas may be weathered feldspar, zeolite, or secondary calcite.
Uses & applications
Widely used as crushed aggregate, road base, railway ballast, riprap, and paving stone; attractive pieces may be used as lapidary or decorative specimens. Common material is low-value.
Geological facts
Basalt makes up much of the oceanic crust and many large volcanic plateaus. Its exact identification would benefit from a fresh broken surface, streak, magnetism test, and magnification.
Field identification & locations
Common in volcanic regions, including Hawaii, Iceland, the Pacific Northwest, India, and ocean-floor environments. It is distinguished from granite by its darker color and much finer grain; a hand lens may reveal tiny interlocking crystals.
