Langbeinites are a family of crystalline substances based on the structure of langbeinite with general formula M 2 M ' 2 (SO 4) 3, where M is a large univalent cation such as potassium, rubidium, caesium, or ammonium), and M ' is a small divalent cation for example (magnesium, calcium, manganese, iron, cobalt, nickel, copper, zinc or …