igneous
Porphyritic Igneous Pebble
Porphyritic Basalt or Rhyolite
AI-generated identification · may be incorrectHardness of 6-7 on Mohs scale, grayish-brown matrix with distinct pinkish feldspar phenocrysts, vitreous to dull luster, cryptocrystalline structure.
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Physical properties
Hardness of 6-7 on Mohs scale, grayish-brown matrix with distinct pinkish feldspar phenocrysts, vitreous to dull luster, cryptocrystalline structure.
Formation & geological history
Formed by multi-stage cooling of magma, initially deep underground allowing large crystals to form, followed by rapid extrusion or shallow intrusion.
Uses & applications
Used primarily as decorative aggregate, landscaping stone, and collected as a natural geological specimen.
Geological facts
The contrasting pink spots are phenocrysts of potassium or plagioclase feldspar that crystallized before the finer-grained matrix.
Field identification & locations
Identify by the striking contrast of lighter phenocrysts embedded in a darker fine-grained groundmass; commonly found in riverbeds and glacial drift.
