igneous
Weathered basaltic rock
Likely vesicular basalt or basaltic andesite; fine-grained plagioclase–pyroxene rock
AI-generated identification · may be incorrectDark gray-brown, dull to slightly earthy luster, uneven fracture, and apparently fine-grained texture with possible weathering pits. Typical hardness is about 5–6 Mohs; cleavage is absent as a whole rock and specific gravity is roughly 2.8–3.1.
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Physical properties
Dark gray-brown, dull to slightly earthy luster, uneven fracture, and apparently fine-grained texture with possible weathering pits. Typical hardness is about 5–6 Mohs; cleavage is absent as a whole rock and specific gravity is roughly 2.8–3.1.
Formation & geological history
Formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, commonly in volcanic flows; the specimen’s exact age cannot be determined from the image.
Uses & applications
Used widely as crushed aggregate, road base, riprap, and occasionally building stone. Ordinary hand specimens generally have little commercial or collector value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust. Brown coloration commonly results from oxidation and surface weathering of iron-bearing minerals.
Field identification & locations
Look for a dense dark color, very fine grains, lack of visible quartz, and possible tiny vesicles; a streak, magnetism, and fresh broken surface would improve identification. Common worldwide, especially volcanic regions and oceanic islands.
