igneous
Porphyritic Basalt
Basalt with Feldspar Phenocrysts
AI-generated identification · may be incorrectHardness: 6 (Mohs scale), Color: Dark gray/black matrix with lighter colored feldspar crystals, Luster: Dull to slightly shiny where wet/fractured, Crystal structure: Fine-grained matrix with larger visible crystals (phenocrysts).
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark gray/black matrix with lighter colored feldspar crystals, Luster: Dull to slightly shiny where wet/fractured, Crystal structure: Fine-grained matrix with larger visible crystals (phenocrysts).
Formation & geological history
Formed from the rapid cooling of basaltic lava at or near the Earth's surface, with larger crystals having formed deeper and slower before eruption.
Uses & applications
Used primarily as crushed stone for construction, road base, and railroad ballast.
Geological facts
The larger crystals (phenocrysts) in porphyritic rocks provide a history of the magma's cooling; slow cooling underground followed by rapid cooling upon eruption.
Field identification & locations
Can be identified by its dark, fine-grained matrix containing distinct, larger crystals. Commonly found in volcanic regions worldwide.
