Potassic white micas were synthesized in the K 2 O-MgO-Al 2 O 3 -SiO 2 -H 2 O system along the pseudobinary join muscovite-aluminoceladonite (mu-Alcel). Composition of run products as measured by electron microprobe analysis are in the range mu 89 -Alcel 11 to mu 01 -Alcel 99 . Cell parameters were determined on powder samples by full-profile Rietveld refinement, using both a single-polytype and a multi-polytype model. The results of both analysis models are in full agreement, and show that the phengite cell parameters have a distinct dependence on the celadonite content: the c parameter shows a monotonic decrease over the full compositional range, whereas the a and b parameters both increase in the Alcel 0 -Alcel 60 range but decrease in the Alcel 60 -Alcel 100 range. The monoclinic b angle decreases slightly with increasing celadonite content. The overall behavior of the cell parameters indicates a decrease of the ditrigonal distortion of the tetrahedral 6-rings, and an increased trioctahedral character of the structure at high celadonite compositions. The molar volume along the solid solution join shows a maximum at about Alcel 30 . Molar volume vs. composition can be fitted by a symmetric function for the excess volume yielding a molar volume for end member aluminoceladonite of 13.957 ± 0.006 J/bar, for muscovite 14.076 ± 0.004 J/bar, and a symmetric positive deviation from ideal volumes of mixing with W = 0.198 ± 0.025 J/bar, and r 2 = 0.941. The use of an asymmetric excess volume function does not significantly improve the fit quality (r 2 = 0.945).

X-ray and neutron diffraction techniques have been applied to quantitative texture analysis of a glaucophanite from the Sesia-Lanzo Zone (Western Italian Alps), naturally deformed under eclogite fades conditions. The comparison has been carried out in order to reveal the limits and proNems of texture analysis related to strongly deformed polymineralic. Different methods of measuring and computing the orientation distribution function from diffraction data have been tested, in particular X-rays, direct peak integration, and neutron diffraction using Rietveld-texture analysis. Due to grain-size problems and heterogeneity of individual amphibole minerals, neutron radiation is shown to be the best probe for characterizing the whole rock: being more penetrative than conventional X-rays, a larger volume of the mineral aggregate is sampled, giving better statistics. However, results obtained by summing the corresponding individual spectra of at least three X-ray diffraction experiments on parallel slabs of the same specimen also give statistically valid, semiquantitative results that reproduce the overall textures. The quantitative texture analysis shows the strong texture of the two generations of amphiboles (AmpI and AmpII), which are mainly characterized by [001]*-directions at an angle of about l0 ° to the mineral lineation and by (hkO) planes describing girdles around the lineation. The texture is comparable to those described in the literature for amphibole deformed under different temperature and pressure conditions, and the pronounced asymmetry of the [001]* directions with respect to the mineral lineation is consistent with a non-coaxial component that occurs during the deformation.