igneous
Granite or granitic gneiss pebble
Quartz–feldspar–mica aggregate; possibly banded gneiss
AI-generated identification · may be incorrectGray, rounded, fine- to medium-grained specimen with visible pale quartz/feldspar and darker biotite or amphibole. Hardness is approximately 6–7 Mohs, nonmetallic luster, interlocking crystals, and no obvious cleavage as a whole rock; specific gravity is roughly 2.6–2.8.
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Physical properties
Gray, rounded, fine- to medium-grained specimen with visible pale quartz/feldspar and darker biotite or amphibole. Hardness is approximately 6–7 Mohs, nonmetallic luster, interlocking crystals, and no obvious cleavage as a whole rock; specific gravity is roughly 2.6–2.8.
Formation & geological history
Likely formed from slowly cooled silica-rich magma (granite) or metamorphosed granite (gneiss), commonly during Precambrian to Paleozoic mountain-building. Its rounded shape indicates later stream, beach, or glacial abrasion.
Uses & applications
Used as aggregate, building stone, paving material, and decorative rock; attractive polished pieces may be sold as inexpensive specimens.
Geological facts
The light and dark mineral patches reflect contrasting quartz/feldspar and mafic minerals. The image does not clearly resolve foliation, so distinguishing granite from gneiss requires a fresh or close-up surface.
Field identification & locations
Look for glassy gray quartz, blocky white feldspar, and black mica; granite is generally massive, while gneiss shows mineral banding. Common worldwide, especially in exposed mountain belts and glacial gravels.
