Near-pristine surfaces of natural pentlandite have been characterized for the first time by X-ray photoelectron spectroscopy (XPS). The Fe 2p, Ni 2p, S 2p and O 1s spectra are discussed, The main feature of interest is found in the S 2p spectrum where two major doublers are found, one with a S 2p(3/2) binding energy of 161.44 eV and the other at 162.19 eV. These doublers are interpreted as being due to sulphur in a 4-coordinate environment and a 5-coordinate environment, respectively, We have obtained a ratio of 1:2.5 for these two species, in reasonable agreement with the theoretical ratio of 1:3 predicted from the pentlandite structure. Natural pentlandite samples have been exposed to de-ionized water for periods of 1.5 and 6 h. The pentlandite surfaces were oxidized to give surfaces that were rich in iron oxyhydroxide species and depleted in nickel and sulphur.