Sulfur, the element S, usually occurs combined in minerals, but the native form is common around volcanoes and in thick underground beds. (more below)
Photo courtesy Michael Tyler of flickr.com under Creative Commons license
Sulfur is predominantly found in sulfide minerals
like pyrite and sulfate minerals
like gypsum. But the element is volatile and is released in vapor around volcanoes. Sulfur gas originates as hydrogen sulfide (H2
S), but that quickly oxidizes to sulfuric acid (H2
) and enters the water cycle, eventually to combine with metal ions and become a sulfide or sulfate mineral, ready for liberation again by a future volcano.
A fraction of this sulfur, though, is preserved in native form, either briefly around gas vents like this beautiful example from White Island Volcano in New Zealand, or in thick beds underground that form by chemical reduction. These were once mined by pumping superheated steam undergound to melt the sulfur, then pumping it out of the ground. Nowadays, sulfur is a byproduct of metal mining and petroleum production.
Other Hydrothermal Vein Minerals