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New experimental data are presented that allows the biotite-magnetite-sanidine equilibrium to be used for estimating water fugacity ([f.sub.[H.sub.2]O]) in hydrous phonolitic magmas. It is also demonstrated that the partly ionic model gives the best estimate for the annite activity ([a.sub.annite]). Crystallization experiments were carried out on a representative sample of peralkaline, phonolitic obsidian of Montana Blanca (MB) pumice deposit, Tenerife, Canary Islands. Experiments were performed from 720-810 [degrees]C and 50-250 MPa. Redox conditions were varied between NNO (nickel + nickel oxide) + 1 ([+ or -]0.2) and FMQ (fayalite + magnetite + quartz). The majority of the experiments were done under [H.sub.2]O saturation conditions ([P.sub.water] = [P.sub.total]). Several experiments were done using a mixed [H.sub.2]O-C[O.sub.2] fluid phase whereas in other experiments 10 or 20 wt% powdered alkali feldspar was added to the starting material. The pre-eruptive [f.sub.[H.sub.2]O] of the Montana Blanca magma is estimated at 676 [+ or -] 200 bars. The pre-emptive [f.sub.[H.sub.2]O] for the Fish Canyon tuff (753-2978 bars) and Bishop tuff rhyolite (1065-2440 bars) were also calculated, as well as [f.sub.[H.sub.2]O] for metamorphic biotite from Au Sable Forks ([approximately equal to] 130 bars). The results of this study suggest that this geohygrometer can be used in any magmatic system in which biotite-magnetite-sanidine is a stable assemblage. Keywords: Crystallization experiments, geohygrometer, pbonolitic magmas, water fugacity

The hydrothermal synthesis and structural characterization of two new germanates with an interesting structure containing double helical Ge-chains and unusual [Ge.sub.4][(OH).sub.4] cubanes is reported. Both germanates keep the same topological novel inorganic framework, which is assembled from [Ge.sub.4][(OH).sub.4] cubane and chiral intertwined Ge-O double helices.

The high levels of mercury resistance merA to Hg (II) found in bacteria isolated form the interface between hydrothermal fluids and oxygenated seawater is studied. The distribution of mercury resistance among the deep-sea strains studied clearly showed that mesophilic and moderately thermophilic strains from the vent and its associated plume were more resistant to Hg(II) than psychrophilic strains collected at the control side.