igneous
Tumbled granite or granitic gneiss pebble
Granite/granitic gneiss, chiefly quartz, feldspar, and dark biotite or amphibole
AI-generated identification · may be incorrectHardness about 6–7 Mohs; cream to pale yellow with black, coarse mineral patches, vitreous to dull luster, and no obvious cleavage on the polished surface. The contrasting granular texture suggests quartz–feldspar rock with mafic minerals.
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Physical properties
Hardness about 6–7 Mohs; cream to pale yellow with black, coarse mineral patches, vitreous to dull luster, and no obvious cleavage on the polished surface. The contrasting granular texture suggests quartz–feldspar rock with mafic minerals.
Formation & geological history
Likely formed from slowly cooled continental magma, or from metamorphosed granite if the dark minerals show banding; such rocks are commonly Precambrian to younger. The rounded shape indicates natural water abrasion or tumbling.
Uses & applications
Used as aggregate, building and paving stone, countertops, landscaping rock, and decorative tumbled material. As a small polished specimen, its value is mainly ornamental or educational.
Geological facts
Granite’s light minerals are usually quartz and feldspar, while black areas are commonly biotite mica or hornblende. A streak test is generally white, and dilute acid should produce no fizz.
Field identification & locations
Common in continental shields and river or glacial gravels worldwide; identify by its interlocking granular texture and mixed light/dark minerals. A close photo of an unpolished surface or a hardness test would distinguish granite from gneiss or other feldspathic rocks.
