The combination of orthoclase feldspar (or microcline), quartz, and either mica, hornblende or augite is termed granite, if the texture is coarse enough so the individual minerals can be recognized with the unaided eye. The rock is light-colored because the feldspar and quartz dominate. Accessory minerals may be present such as apatite, zircon, beryl or magnetite. Varieties of granite are distinguished according to the dark mineral present. When this is muscovite, it is a _muscovite-granite_; when it is biotite, a _biotite-granite_; if it is hornblende, a _hornblende-granite_; etc. The size of crystals in granite varies widely. When they are as small as ¹/₁₂ of an inch in diameter, it is termed fine grained; from ¹/₁₂ to ¼ of an inch, it is medium-grained; when larger, it is coarse-grained. In some cases the crystals may be over a foot in diameter which is known as _giant granite_. Originally granite was a great mass of molten magma, which has cooled very slowly, having been intruded or thrust up in great stocks or batholiths beneath overlying rocks, which acted as a blanket to prevent rapid cooling. These overlying rocks, in their turn, have been acted upon by the heat and metamorphosed. Granite is particularly likely to have been formed under mountain folds; so that, after the mountains have been more or less completely eroded away, the great masses of granite have come to the surface to mark the axes of the ranges; and even after the mountains have been wholly worn away, the granite remains to mark the sites on which they stood. In the granite mass itself, there are often veins and dikes, which probably resulted from the shrinkage of the cooling granite, and they are filled with a different and usually coarser granite known as pegmatite. This pegmatite formed from the residual magmatic material, so that as some of the elements had already crystallized out, the granite in these dikes is of different composition. The extreme coarseness of these pegmatites seems to be due to the character of the mineralizing agents left in the dikes. In some of these pegmatites the feldspar and quartz are so intergrown, that when broken along the cleavage surface of the feldspar, the quartz appears like cuneiform characters, and this variety has been given the name _graphic granite_ (See Plate 53).