igneous
Polished porphyritic granite pebble
Granite, likely biotite- or hornblende-bearing; composition dominated by quartz, feldspar, and dark mafic minerals
AI-generated identification · may be incorrectHardness about 6–7 Mohs; pink-gray to brown, granular, with visible interlocking crystals and dark mineral speckles; vitreous to dull luster, no obvious cleavage as a whole, and typical specific gravity of 2.6–2.8.
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Physical properties
Hardness about 6–7 Mohs; pink-gray to brown, granular, with visible interlocking crystals and dark mineral speckles; vitreous to dull luster, no obvious cleavage as a whole, and typical specific gravity of 2.6–2.8.
Formation & geological history
An intrusive igneous rock that crystallized slowly from silica-rich magma deep in the crust, commonly during Precambrian to younger continental plutonism; the rounded form results from stream or beach transport and abrasion, with later polishing possible.
Uses & applications
Used as aggregate, building stone, countertops, monuments, landscaping rock, and decorative tumbled specimens; this small pebble has modest collector value.
Geological facts
The mottled pattern reflects large feldspar and quartz grains set among darker biotite or amphibole. Exact identification would require a close-up or thin section because weathering and lighting obscure mineral boundaries.
Field identification & locations
Common worldwide, especially in continental shields and granitic mountain regions. Field clues include coarse interlocking grains, pink/white feldspar, gray translucent quartz, and black mica or amphibole; it should not fizz with dilute acid.
