igneous
Blue-gray granite or granitic gneiss pebble
Granite, chiefly quartz, feldspar, and biotite/amphibole
AI-generated identification · may be incorrectHardness about 6–7 Mohs; blue-gray, granular, and speckled with a dull to glassy luster. Interlocking crystals are visible, but the small rounded specimen prevents confident identification of cleavage or specific gravity.
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Physical properties
Hardness about 6–7 Mohs; blue-gray, granular, and speckled with a dull to glassy luster. Interlocking crystals are visible, but the small rounded specimen prevents confident identification of cleavage or specific gravity.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the crust during an ancient Precambrian to Phanerozoic event, then exposed and rounded by weathering and transport. Exact age and origin cannot be determined from the photograph.
Uses & applications
Granite is widely used as crushed aggregate, building stone, monuments, countertops, and decorative gravel; this small pebble has mainly educational or modest collecting value.
Geological facts
The blue appearance may result from blue-gray quartz, feldspar, or lighting rather than a distinct blue mineral. A true gneiss would show mineral banding, which is not clearly visible here.
Field identification & locations
Identify it by its coarse interlocking texture, mixed light and dark grains, and inability to scratch with a steel knife (though quartz can scratch glass). Common in glacial deposits, stream gravels, and areas near granite bedrock.
