igneous
Porphyritic Basalt or Amygdaloidal Basalt
Porphyritic Extrusive Igneous Rock
Hardness of 6-7 on the Mohs scale, greenish-grey groundmass with distinct brownish or weathered phenocrysts/vesicles filled with secondary minerals, dull to sub-vitreous luster, aphanitic texture with coarser crystals.
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Physical properties
Hardness of 6-7 on the Mohs scale, greenish-grey groundmass with distinct brownish or weathered phenocrysts/vesicles filled with secondary minerals, dull to sub-vitreous luster, aphanitic texture with coarser crystals.
Formation & geological history
Formed from volcanic lava flows that cooled in two stages: slowly beneath the surface allowing larger crystals (phenocrysts) to form, followed by rapid cooling on the Earth's surface.
Uses & applications
Used in construction, road aggregate, and as a decorative stone or lapidary specimen for collectors.
Geological facts
Porphyritic textures indicate a complex cooling history where magma chambers underwent changes in temperature or pressure before erupting.
Field identification & locations
Can be identified in the field by its fine-grained dark or greenish matrix dotted with distinct larger crystals or spots. Commonly found in volcanic regions worldwide.
