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.