Original: Volcanoes and some hot springs (as well as cold springs) emit some H2S, where it probably arises via the hydrolysis of sulfide minerals, i.e. MS + H2O â 'MO + H2S.
Simplified: Volcanoes and hot springs emit some H2S, where it probably arises via the hydrolysis of sulfide minerals, i.e. MS + H2O to give MO + H2S.