igneous
Porphyritic basalt (likely)
Porphyritic basalt; plagioclase-rich volcanic rock, with composition varying by specimen
AI-generated identification · may be incorrectDark gray, fine-grained groundmass with abundant pale, likely plagioclase crystals; rough, uneven fracture and no obvious cleavage. Approximate hardness 5–6 Mohs; typically dull to slightly vitreous, with feldspar crystals in a fine matrix.
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Physical properties
Dark gray, fine-grained groundmass with abundant pale, likely plagioclase crystals; rough, uneven fracture and no obvious cleavage. Approximate hardness 5–6 Mohs; typically dull to slightly vitreous, with feldspar crystals in a fine matrix.
Formation & geological history
Formed when basaltic lava cooled, with larger crystals growing before the remaining melt cooled rapidly. The image alone does not establish its age or exact composition.
Uses & applications
Primarily a geological or educational specimen; basalt is widely used as crushed aggregate, road stone, and construction material.
Geological facts
The contrasting larger crystals indicate a porphyritic texture, recording a two-stage cooling history.
Field identification & locations
Look for pale feldspar crystals set in a darker, compact volcanic matrix; a fresh surface and mineral tests would be needed to confirm basalt versus another porphyritic igneous rock. Basalt occurs worldwide in volcanic regions and oceanic crust.
