igneous
Weathered granite or granitic gneiss cobble
Granite; chiefly quartz, feldspar, and biotite/hornblende
AI-generated identification · may be incorrectMedium- to coarse-grained, gray, speckled rock with dark mafic minerals and a dull weathered luster; hardness about 6–7 Mohs, massive texture, and no obvious cleavage as a whole. The rounded shape suggests natural transport or prolonged weathering.
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Physical properties
Medium- to coarse-grained, gray, speckled rock with dark mafic minerals and a dull weathered luster; hardness about 6–7 Mohs, massive texture, and no obvious cleavage as a whole. The rounded shape suggests natural transport or prolonged weathering.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the continental crust, commonly during Precambrian to younger continental mountain-building events; surface rounding and dark staining reflect weathering and abrasion.
Uses & applications
Common granite is used for crushed aggregate, road stone, building blocks, paving, monuments, and countertops; this rounded specimen has mainly educational or landscaping value.
Geological facts
Granite’s visible grains formed because magma cooled slowly underground. Dark patches may be biotite-rich zones, hornblende, weathering stains, or lichen rather than a separate rock type.
Field identification & locations
Identify it by interlocking visible quartz and feldspar grains, gray color, and scattered black mica or amphibole; a glassy surface or strong foliation would suggest another material. Common worldwide, especially in continental shields and mountain belts.
