igneous
Basaltic rock fragment (likely vesicular basalt)
Basalt; chiefly plagioclase, pyroxene, and possibly olivine
AI-generated identification · may be incorrectDark gray-black, fine-grained and dull to slightly glassy, with small irregular pores and pale mineral grains; hardness about 5–6 Mohs, generally massive with no visible cleavage, and specific gravity about 2.8–3.0.
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Physical properties
Dark gray-black, fine-grained and dull to slightly glassy, with small irregular pores and pale mineral grains; hardness about 5–6 Mohs, generally massive with no visible cleavage, and specific gravity about 2.8–3.0.
Formation & geological history
Formed when low-silica mafic lava cooled rapidly at or near Earth’s surface, commonly in volcanic flows; its exact geological age cannot be determined from the image.
Uses & applications
Used extensively as crushed aggregate, road stone, rail ballast, and building stone; small attractive pieces have modest specimen value.
Geological facts
The rounded shape may result from natural abrasion, weathering, or tumbling. Pale grains may be plagioclase, while dark grains are likely pyroxene or olivine.
Field identification & locations
Identify basalt by its dense dark color, fine texture, and mafic mineral speckles; vesicles support a volcanic origin. Common worldwide in volcanic regions, including Hawaii, Iceland, India, and oceanic crust.
