igneous
Porphyritic Basalt
Extrusive igneous rock with phenocrysts
AI-generated identification · may be incorrectHardness 6 on Mohs scale; brownish-weathered groundmass with distinct lighter and darker phenocrysts; aphanitic texture with visible larger crystals.
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Physical properties
Hardness 6 on Mohs scale; brownish-weathered groundmass with distinct lighter and darker phenocrysts; aphanitic texture with visible larger crystals.
Formation & geological history
Formed from cooling lava flows where minerals began crystallizing beneath the surface before rapid cooling on the surface froze the fine-grained matrix.
Uses & applications
Used as crushed stone in construction, road aggregate, and dimension stone.
Geological facts
The distinct contrast between large crystals and the fine matrix is a classic example of two-stage cooling history in volcanic environments.
Field identification & locations
Identify by the speckled appearance of contrasting crystal grains embedded in a weathered brownish volcanic groundmass; commonly found in ancient lava flows worldwide.
