igneous
Weathered basalt (likely amygdaloidal basalt)
Basalt; chiefly plagioclase feldspar and pyroxene, with possible olivine and iron oxides
AI-generated identification · may be incorrectFine-grained, dark gray-green to brown, dull to faintly granular luster, commonly massive; Mohs hardness about 6. Small reddish-brown and pale spots may be weathering products or vesicle fillings, but crystal identity cannot be confirmed from the image.
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Physical properties
Fine-grained, dark gray-green to brown, dull to faintly granular luster, commonly massive; Mohs hardness about 6. Small reddish-brown and pale spots may be weathering products or vesicle fillings, but crystal identity cannot be confirmed from the image.
Formation & geological history
An extrusive igneous rock formed when mafic lava cooled rapidly at or near Earth’s surface, commonly in volcanic flows; its precise age and locality cannot be determined visually. Green-brown coloration likely reflects surface weathering and alteration.
Uses & applications
Used as crushed aggregate, roadstone, riprap, building stone, and occasionally as a decorative material; this weathered hand specimen has little commercial value.
Geological facts
Basalt is the most abundant volcanic rock in oceanic crust and commonly forms at mid-ocean ridges and hotspot volcanoes. Vesicles, if present, formed from gas bubbles trapped during cooling.
Field identification & locations
Identify it by its heavy, fine-grained, dark mafic appearance and lack of obvious quartz; a streak, hardness, acid, and thin-section test would help distinguish altered basalt from andesite or greenstone. Common worldwide, especially volcanic regions and oceanic terrains.
