igneous
Weathered granite cobble
Granite, typically quartz–alkali feldspar–plagioclase with biotite or hornblende
AI-generated identification · may be incorrectCoarse, interlocking crystalline texture; cream-gray with brown iron-oxide staining and weak speckled luster. Hardness about 6–7 Mohs, no true cleavage as a rock, and approximate specific gravity 2.63–2.75.
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Physical properties
Coarse, interlocking crystalline texture; cream-gray with brown iron-oxide staining and weak speckled luster. Hardness about 6–7 Mohs, no true cleavage as a rock, and approximate specific gravity 2.63–2.75.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in continental crust, commonly during Precambrian to Phanerozoic mountain-building events; this rounded specimen was likely shaped by stream or beach transport and weathering.
Uses & applications
Used extensively as dimension stone, countertops, paving, monuments, aggregate, and landscaping rock; this ordinary cobble has little jewelry use.
Geological facts
The visible dark patches may be biotite, hornblende, or weathered mafic inclusions, while rusty tones are likely oxidized iron-bearing minerals.
Field identification & locations
Identify it by visible quartz and feldspar grains, hardness, and lack of layering or foliation; common worldwide, especially in continental shields and mountain belts. A streak test is usually white, and acid produces no reaction.
