Most tochilinite in serpentinites is reported from rocks that, although not deeply weathered themselves, lie immediately below weathered horizons. These include both subaerial and submarine occurrences (van de Vusse and Powell, 1983; Alt and Shanks, 1998). At Holes 1068A, 897C, and 897D on the Iberia Abyssal Plain (Fig. F1), tochilinite is common in serpentinites that occur in a zone beneath rocks containing calcite with pyrite and/or marcasite and above rocks containing more reduced, S-poor minerals (e.g. awaruite) (Alt and Shanks, 1998; Beard and Hopkinson, 2000). This zone appears to be at least 20 m thick at Site 1068 (i.e. comprising Cores 173-1068A-21R and 22R). At Site 1068, tochilinite is interpreted as reflecting a transition in fluid chemistry from reduced, S-poor fluids in the lower serpentinites to more oxidized, S-rich, (seawater-dominated?) fluids closer to the surface (see Beard and Hopkinson, 2000). The change in tochilinite chemistry, from S-poor brucite varieties at depth to S-rich carbonate varieties upsection is consistent with this interpretation.