Inorganic sulfates are formed by reaction of the acid with metals, their oxides or carbonates, or by oxidation of sulfides or sulfites (see sulfur). Most sulfates are soluble in water, the main exceptions being calcium, strontium, barium, and lead sulfates. They decompose at high temperatures to give sulfur trioxide and dioxide. Sulfates form ligand complexes and soluble salts (see alum). Many sulfate minerals occur in nature, often as evaporites or from oxidation of sulfides (see anhydrite; barite; Epsom salts; gypsum).
Bisulfates contain the ion HSO4-; they are acid, and are converted to pyrosulfates (S2O7)21) on heating.
Organic sulfates have the formula R2SO4, where R is an organic group.