Sulfate is a compound composed of sulfate ion (SO42-) and other metal ions. It is an electrolyte, and most of it is soluble in water. Sulfate minerals are salts formed by the combination of metal cations (including ammonium) and sulfate. Because sulfur is a variable valence element, it can form different minerals in different valence states in nature. When it combines the highest valence S6 + with four O 2 - to form SO42 -, and then with metal cations, it forms sulfate. In sulfate minerals, there are more than 20 kinds of metal cations combined with sulfate radical. That is to say, sulfate is the salt containing sulfate.