igneous
Porphyritic basalt
Basalt with pink potassium-feldspar phenocrysts; likely alkaline or trachybasaltic composition
AI-generated identification · may be incorrectDark fine-grained groundmass with scattered pink-orange feldspar crystals and minor pale/green alteration minerals; hardness about 5.5–6.5, generally dull to weakly vitreous, massive, and lacking cleavage as a whole.
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Physical properties
Dark fine-grained groundmass with scattered pink-orange feldspar crystals and minor pale/green alteration minerals; hardness about 5.5–6.5, generally dull to weakly vitreous, massive, and lacking cleavage as a whole.
Formation & geological history
An extrusive volcanic rock formed when basaltic lava cooled rapidly at or near Earth’s surface; individual feldspar crystals grew before eruption. Its exact geological age cannot be determined from the image.
Uses & applications
Used as crushed aggregate, road metal, riprap, and occasionally decorative stone; attractive specimens are collected but are not usually gem-grade.
Geological facts
The large contrasting crystals are phenocrysts, revealing a two-stage cooling history: slow crystallization underground followed by rapid surface cooling.
Field identification & locations
Identify it by its black, fine-grained matrix and conspicuous salmon-pink feldspar spots; confirm with a hand lens and hardness test, while distinguishing it from porphyritic andesite or rhyolite by its very dark matrix. Common in volcanic provinces worldwide.
