The granites are thoroughly crystalline rocks, of typically granitoid texture, to which they have given the name, and without any ground mass. The grains have not their proper crystalline shape, the separate minerals interfering with each other in the process of crystallization. The characteristic minerals are quartz, orthoclase, some acid plagioclase, muscovite, biotite, and hornblende; magnetite and apatite are always present, though in small quantities. The variations in granite are principally in the ferro-magnesian minerals. Thus we have Muscovite granite, with white mica only; granitite, with biotite only; hornblende granite, the hornblende replacing the mica, or in addition to biotite; augite granite, with augite and biotite. Those in which the percentage of soda is high are called soda-granites. When the ferro-magnesian silicates are all absent, the rock is called a binary granite, or Aplite.
The colour of granite is dark or light in accordance with the proportion of dark silicates present, while the shades of the felspar determine whether the rock shall be red, pink, or white. The texture of granite varies from fine to very coarse, and in some cases becomes nearly porphyritic. A very coarse-grained granite is called Pegmatite, or giant granite.