granite (scientific definition)
A visibly granular, crystalline rock of predominantly interlocking texture composed essentially of alkalic feldspars and quartz. Feldspar is generally present in excess of quartz, and accessory minerals (chiefly micas, hornblende, or more rarely pyroxene) are commonly present. The alkalic feldspars may be present (1) as individual mineral species, (2) as isomorphous or mechanical intergrowths with each other, or (3) as chemical intergrowths with the lime feldspar molecule, but 80 + 3% of the feldspar must be composed of the potash or soda feldspar molecules. (Marble Institute, 2011)