The iron-titanium oxide minerals of three troctolites from the Freetown layered gabbro have been analysed using an electron microprobe. Comparisons of the analyses of the iron-titanium minerals with the data of Buddington and Lindsley (I964) provide temperature and oxygen fugacity information relating to particular magnetite-ilmenite grains. Magnetite-ilmenite grains occurring in different sili...

The origin in rocks of the common iron sulphides, pyrrhotine, Fe 1 xS and pyrite, FeS2 and their behaviour during geochemical processes is best considered using the simplified redox reaction: 2FeS ~-~ FeS2 + Fe 2 + + 2e . Thus pyrrhotine is more reduced than pyrite and is the stable iron sulphide formed from magmas except where relatively high oxygen fugacities result from falling pressure or h...

Abstract Apatite is a common accessory mineral in igneous rocks, and its ability to readily accommodate wide range of trace elements means that it may provide useful record magmatic composition processes. Relative abundances redox sensitive apatite could also much-needed probe oxygen fugacity, fO2. Here, examination large data set whole rock compositions used assess the recently proposed, incre...

Hydrogen concentration gradients reported in olivines from several peridotite xenoliths (Demouchy, 2004; Peslier and Luhr, 2006) have been interpreted as evidence of hydrogen loss during ascent to the surface. However, a review of hydrogen diffusion data in anhydrous minerals (Ingrin and Blanchard, 2006) provides new constraints on the possible origin of these heterogeneities. The amount of hyd...