igneous
Granite (likely weathered cobble)
Granite; chiefly quartz, potassium feldspar, plagioclase, and biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, speckled gray-brown rock with visible interlocking crystals; quartz gives a glassy luster, feldspar is pale, and dark minerals are black-brown. Hardness is approximately 6–7 Mohs; massive, with no obvious cleavage as a whole, and specific gravity about 2.6–2.7.
Identified More igneous →
Explore Granite (likely weathered cobble) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Coarse-grained, speckled gray-brown rock with visible interlocking crystals; quartz gives a glassy luster, feldspar is pale, and dark minerals are black-brown. Hardness is approximately 6–7 Mohs; massive, with no obvious cleavage as a whole, and specific gravity about 2.6–2.7.
Formation & geological history
An intrusive igneous rock formed when silica-rich magma cooled slowly deep within Earth, allowing large crystals to grow. Its exact age cannot be determined from the image and may range from Precambrian to much younger depending on locality.
Uses & applications
Widely used for building stone, countertops, paving, monuments, aggregate, and landscaping; attractive polished pieces are sometimes collected, but this rounded cobble has modest value.
Geological facts
The rounded shape indicates prolonged abrasion in a river, beach, or glacial environment rather than its original bedrock form. Surface weathering may darken biotite and stain feldspar brown.
Field identification & locations
Identify it by the visible quartz-and-feldspar mosaic, hardness, and lack of layering or vesicles; a streak test is usually unhelpful. Common worldwide in continental crust and stream gravels; acid produces little or no reaction.
