Although syenite is similar to granite in many regards, the rock contains little or no quartz. Indeed, essentially syenite is comprised of a ferromagnesian mineral and an alkali feldspar, although some varieties also contain a feldspathoid mineral. The exact type of these basic components may vary significantly, and many syenites are named or classified by the dominant mineral they contain. Hedenbergite syenite, for instance, is a type of syenite that contains significant amounts of hedenbergite, a member of the pyroxene family of minerals. Hedenbergite, which is usually dark green or black in color, is a calcium magnesium silicate that is closely related to diopside.