igneous
Polished porphyritic granite
Porphyritic granitoid, composed mainly of quartz, feldspar, and mica
AI-generated identification · may be incorrectCoarse, irregular crystals and larger pale feldspar crystals in a darker matrix; mineral hardness is typically 6–7 Mohs, with vitreous quartz and feldspar luster. The polished surface obscures exact grain boundaries and identification details.
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Physical properties
Coarse, irregular crystals and larger pale feldspar crystals in a darker matrix; mineral hardness is typically 6–7 Mohs, with vitreous quartz and feldspar luster. The polished surface obscures exact grain boundaries and identification details.
Formation & geological history
Formed when silica-rich magma cooled slowly underground, allowing visible crystals to grow; the specific geological age and source cannot be determined from the image.
Uses & applications
Commonly used as a decorative stone, countertop or building material, and polished collectible specimen.
Geological facts
The contrasting large crystals set within a finer-looking groundmass give the rock its porphyritic texture.
Field identification & locations
Look for interlocking grains, glassy gray quartz, pale feldspar, and dark mica or other minerals. Similar granitoids occur worldwide; the pictured hand-sized polished piece may sell for about $5–$25, depending on size and workmanship.
