igneous
Weathered basaltic rock
Basalt, likely amygdaloidal or altered basalt
AI-generated identification · may be incorrectDark gray to brown, fine-grained volcanic rock with rusty iron-oxide weathering and possible vesicles/amygdules. Typical hardness is about 6 Mohs, dull to slightly vitreous luster, massive texture, and no obvious cleavage; density is roughly 2.7–3.1 g/cm³.
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Physical properties
Dark gray to brown, fine-grained volcanic rock with rusty iron-oxide weathering and possible vesicles/amygdules. Typical hardness is about 6 Mohs, dull to slightly vitreous luster, massive texture, and no obvious cleavage; density is roughly 2.7–3.1 g/cm³.
Formation & geological history
Basalt forms when low-silica lava rapidly cools at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and flood-basalt provinces. The orange-brown surface reflects oxidation and prolonged weathering; its exact age cannot be determined from the image.
Uses & applications
Common basalt is used as crushed aggregate, roadstone, riprap, building stone, and occasionally landscaping material. It has little jewelry value unless it contains attractive cavities, agate, zeolite, or other secondary minerals.
Geological facts
The specimen’s irregular rounded shape and contrasting dark and rusty zones are consistent with weathered basalt, though an altered mafic metamorphic rock is also possible without testing.
Field identification & locations
Look for a very fine grain, dark streak, heavy feel, and resistance to scratching by a steel knife; it should not fizz strongly with dilute hydrochloric acid. Common worldwide, especially in volcanic regions; a fresh surface and thin-section or chemical testing would improve identification.
