igneous
Vesicular basalt (possibly scoriaceous basalt)
Mafic volcanic rock; primarily plagioclase, clinopyroxene, olivine, and volcanic glass
AI-generated identification · may be incorrectDark reddish-brown, fine-grained and vesicular, with a dull to subtly sparkling luster from exposed crystals. Typically Mohs 5–6, massive, with no cleavage; rounded surfaces indicate weathering or abrasion, and the pale metallic-looking grains may be feldspar or pyroxene rather than metal.
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Physical properties
Dark reddish-brown, fine-grained and vesicular, with a dull to subtly sparkling luster from exposed crystals. Typically Mohs 5–6, massive, with no cleavage; rounded surfaces indicate weathering or abrasion, and the pale metallic-looking grains may be feldspar or pyroxene rather than metal.
Formation & geological history
Forms when basaltic lava rapidly cools at or near Earth’s surface, trapping gas bubbles; the red-brown color commonly reflects oxidation of iron-bearing minerals. Basalt forms throughout geologic time, especially at volcanic fields, mid-ocean ridges, and hotspots.
Uses & applications
Used as aggregate, road base, ballast, riprap, landscaping stone, and occasionally decorative material; usually has little jewelry value.
Geological facts
Vesicles are gas bubbles preserved in lava, while denser basalt lacks them. Its magnetic response may be detectable if magnetite is abundant.
Field identification & locations
Common in Hawaii, Iceland, the Pacific Northwest, India’s Deccan Traps, and many volcanic regions worldwide; identify by its dark mafic color, fine texture, vesicles, and hardness. Typical specimen value is $3–$20, or up to $30–$75 for attractive polished or locality-labeled pieces.
