igneous
Rounded granite cobble
Granite, likely biotite granite or granodiorite
AI-generated identification · may be incorrectCoarse-grained, speckled tan-gray rock with quartz, feldspar, and dark mica; generally Mohs 6–7, vitreous quartz luster, massive texture, and no cleavage as a whole. Rounded edges indicate stream or beach abrasion; exact mineral proportions are uncertain from the photograph.
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Physical properties
Coarse-grained, speckled tan-gray rock with quartz, feldspar, and dark mica; generally Mohs 6–7, vitreous quartz luster, massive texture, and no cleavage as a whole. Rounded edges indicate stream or beach abrasion; exact mineral proportions are uncertain from the photograph.
Formation & geological history
Formed by slow cooling of silica-rich magma deep in the continental crust, commonly during Precambrian to Phanerozoic mountain-building events. Later erosion transported and rounded the fragment.
Uses & applications
Used widely as dimension stone, countertops, monuments, paving, aggregate, and landscaping stone; this small cobble has little commercial or jewelry value.
Geological facts
The orange-tan color likely comes from weathered potassium feldspar, while black flecks are probably biotite or hornblende. Granite commonly shows visible interlocking crystals rather than layers or vesicles.
Field identification & locations
Identify it by its granular interlocking texture, quartz translucence, feldspar crystals, and dark mica; it is common in granitic terrains and gravel deposits worldwide. A hand lens and dilute acid test (typically no reaction) can help distinguish it from limestone.
