igneous
Probable amygdaloidal basalt
Basalt, a fine-grained mafic volcanic rock; exact identification is uncertain from the close-up image
AI-generated identification · may be incorrectDark gray to black, fine-grained groundmass with pale rounded spots that may be mineral-filled vesicles. Basalt typically has Mohs hardness about 6, a dull to slightly vitreous luster, and no visible cleavage; the spots cannot be identified confidently from the image.
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Physical properties
Dark gray to black, fine-grained groundmass with pale rounded spots that may be mineral-filled vesicles. Basalt typically has Mohs hardness about 6, a dull to slightly vitreous luster, and no visible cleavage; the spots cannot be identified confidently from the image.
Formation & geological history
Forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface. Vesicles form as gas escapes; later mineral deposits may fill them, with age depending on the specific flow.
Uses & applications
Basalt is widely used as crushed aggregate, road stone, and building stone; specimens with attractive mineral-filled cavities are collected.
Geological facts
A vesicle-filled basalt is called vesicular basalt; when cavities are filled by secondary minerals, it is termed amygdaloidal basalt.
Field identification & locations
Look for a dense, dark volcanic matrix and rounded cavities or pale fillings; confirm with a fresh surface and mineral tests. Basalt occurs worldwide in volcanic regions, including oceanic crust and lava plateaus.
