igneous
Granite cobble
Granite, a coarse-grained felsic intrusive igneous rock, chiefly quartz, potassium feldspar, plagioclase, and dark biotite or hornblende
AI-generated identification · may be incorrectSpeckled gray-and-white with dark minerals; visible interlocking crystals and no layering. Typical hardness is about 6–7 Mohs; minerals are mostly vitreous, with no consistent rock-wide cleavage; specific gravity is roughly 2.6–2.8.
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Physical properties
Speckled gray-and-white with dark minerals; visible interlocking crystals and no layering. Typical hardness is about 6–7 Mohs; minerals are mostly vitreous, with no consistent rock-wide cleavage; specific gravity is roughly 2.6–2.8.
Formation & geological history
Magma cooled slowly beneath the crust, allowing crystals to grow. Granite forms in continental crust across many geological ages; this rounded specimen’s age and source cannot be determined from the image.
Uses & applications
Used as dimension stone, paving, countertops, monuments, and aggregate; attractive cobbles are also collected or used in landscaping.
Geological facts
The black-and-white “salt-and-pepper” appearance comes from light feldspar and quartz contrasting with dark mica or amphibole.
Field identification & locations
The rounded shape indicates water or other transport and abrasion; identify granite by its visible interlocking quartz and feldspar grains. Similar rocks occur widely in continental regions, but exact locality needs geological context.
