igneous
Vesicular Basalt / Lava Rock
Extrusive mafic igneous rock (Mafic silicate)
Hardness 5-6 Mohs. Color is dark grey to black. Luster is dull to sub-vitreous. Texture is vesicular with small cavities formed by gas bubbles trapped during rapid cooling. Fine-grained (aphanitic) matrix composed mostly of plagioclase feldspar and pyroxene.
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Physical properties
Hardness 5-6 Mohs. Color is dark grey to black. Luster is dull to sub-vitreous. Texture is vesicular with small cavities formed by gas bubbles trapped during rapid cooling. Fine-grained (aphanitic) matrix composed mostly of plagioclase feldspar and pyroxene.
Formation & geological history
Formed from rapid cooling of low-viscosity, gas-rich basaltic lava erupted at Earth's surface or underwater. As lava depressurizes, expanding gas bubbles create voids (vesicles) before the rock solidifies.
Uses & applications
Widely used in landscaping, gas grill lava rocks, aquariums, drainage systems, lightweight concrete aggregates, and sauna heating stones.
Geological facts
Basalt is the most common rock type in Earth's crust, forming the bulk of oceanic crust. Similar vesicular basaltic rocks compose vast areas of the Moon (lunar maria) and Mars.
Field identification & locations
Identify by its dark charcoal-to-black color, relatively low density compared to solid basalt, and pitted surface full of small rounded cavities (vesicles). Found abundantly near volcanic regions such as Hawaii, Iceland, and the Pacific Northwest.
