Sulfur occurs mainly in the sulfate form, as, for example, the calcium sulfate (anhydrite), magnesium sulfate (Epsom salt and kyeserite), barium sulfate (barite), strontium sulfate (celestite), and sodium sulfate (glauberite). All the spring waters have the sulfate ion and some have also hydrogenate-sulfide (sulfuric waters).

This element can also be found, in the form of metallic sulfides, in pyrite, calcopyrite, galena, blende, rosalgar and the cinnabar. Volcanic gases contain sulfur dioxide and hydrogen sulfide, which can also be found dissolved in the sulfuric waters.

The most important sources of sulfur are the mines of sulfur in the native state that can be found mainly in the USA (Louisiana and Texas), and in Japan. In Europe, the main deposits are in Sicily. In Spain, there are deposits in the Mountain of Gador (Almeria). In Portugal, it occurs in the Furnas of S. Miguel (Azores).