Kesterite is the Zn-rich variety whereas the Zn-poor form is called ferrokesterite or stannite. Owing to their similarity, kesterite is sometimes called isostannite.[4] The synthetic form of kesterite is abbreviated as CZTS (from copper zinc tin sulfide). The name kesterite is sometimes extended to include this synthetic material and also CZTSe, which contains selenium instead of sulfur.[5][6]