igneous
Speckled granitic pebble
Granite or granitic gneiss; quartz–feldspar–mica aggregate
AI-generated identification · may be incorrectHardness about 6–7 Mohs; light gray-white with black and brown speckles, granular texture, and dull to vitreous luster. Interlocking crystals are visible, with no obvious cleavage on the rounded surface; specific gravity is typically 2.6–2.8.
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Physical properties
Hardness about 6–7 Mohs; light gray-white with black and brown speckles, granular texture, and dull to vitreous luster. Interlocking crystals are visible, with no obvious cleavage on the rounded surface; specific gravity is typically 2.6–2.8.
Formation & geological history
Formed by slow cooling of silica-rich magma deep underground, producing coarse crystals; comparable granites commonly formed during Precambrian to younger continental episodes. The pebble was later weathered and rounded by stream or shoreline transport.
Uses & applications
Used as crushed aggregate, building stone, countertops, monuments, and decorative gravel; small pieces have modest collecting value.
Geological facts
The dark grains are likely biotite or amphibole, while pale grains are feldspar and quartz. Its rounded shape indicates mechanical erosion rather than crystal growth in place.
Field identification & locations
Identify it by its hard, speckled, interlocking crystalline texture and inability to scratch easily with a steel knife; vinegar will not fizz. Common in glacial deposits, riverbeds, beaches, and granite terrains.
