List the important sources of sulphur.
Sulphur generally exists in the combined form in the following sulphate minerals like gypsum (CaSO4.2H2O), Epsom salt (MgSO4.7H2O), barite (BaSO4) and sulphide minerals such as galena (PbS), zinc blende (ZnS), copper pyrites (CuFeS2). Traces of sulphur are present in volcanoes as hydrogen sulphide. Sulphur is also present in organic materials such as eggs, proteins, garlic, onion, mustard, hair, and wool.