Group of minerals that contains one or more metallic element in addition to the sulfate radical (SO4). All sulfates are transparent to translucent and soft. Most are heavy and lightly colored, and some are soluble in water. Rarer sulfates exist containing substitutions for the sulfate radical, such as the chromates, where it is replaced by a chromate radical (CrO4). The sulfates can be divided into the Hydrous sulfates and the Anhydrous sulfates. The chromates are usually classified as a sub-group of the sulfates.