igneous
Weathered volcanic rock, likely vesicular basalt
Basalt, primarily plagioclase feldspar, pyroxene, and commonly olivine; surface altered to iron-bearing clay minerals
AI-generated identification · may be incorrectDark brown-gray, dull to faintly earthy luster, fine-grained, irregular vesicles and weathering cavities, with no visible crystals. Hardness is approximately 5–6 Mohs; massive basalt has no cleavage and typical specific gravity near 2.8–3.0.
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Physical properties
Dark brown-gray, dull to faintly earthy luster, fine-grained, irregular vesicles and weathering cavities, with no visible crystals. Hardness is approximately 5–6 Mohs; massive basalt has no cleavage and typical specific gravity near 2.8–3.0.
Formation & geological history
Basalt forms when low-silica lava cools rapidly at or near Earth’s surface, commonly in volcanic flows; this specimen’s rounded shape and cavities indicate prolonged weathering or transport. Its exact geological age cannot be determined from the photograph.
Uses & applications
Common basalt is used as crushed aggregate, road stone, riprap, and building stone; attractive pieces may be collected, but this example has little jewelry value.
Geological facts
The holes are vesicles or weathering voids, originally formed by escaping gas or later mineral dissolution. Brown coloration likely reflects oxidation of iron-bearing minerals.
Field identification & locations
Look for a dense, fine-grained dark interior, scattered vesicles, and a relatively heavy feel; a streak, hardness, and fresh broken surface would help confirm basalt. Basalt occurs worldwide, especially in volcanic regions and oceanic crust.
