Electron microprobe analyses are presented for astrophyllite-group minerals from hydrothermal veins and pegmatites of the Ilimaussaq complex, South Greenland. The analyses fall mainly into two groups: (1) niobophyllites with the highest Nb/(Nb+Ti) ratios yet recorded (∼0.9), occurring only in the veins, and (2) an essentially continuous sequence from astrophyllite to niobophyllite with Nb/(Nb+Ti) up to 0.6, found in veins and pegmatites. It is highly likely that there is complete solid solution between astrophyllite and niobophyllite. More limited substitution of Mn for Fe has resulted in the formation of kupletskite in some rocks. Altered zones in certain astrophyllites and niobophyllites have compositional features similar to the type ‘hydroastrophyllite’. The astrophyllite-group minerals in the hydrothermal veins crystallized at temperatures below 400°C at 1 kbar and under high pH and low oxygen fugacity, whereas those in the pegmatites were formed from water-rich melts which were hotter (≥450°C), less basic and more oxidized.

Accessory tourmaline in metasediments from the Sinai crystalline basement exhibits textural and chemical signatures that relate to the evolution of regional metamorphism and deformation during the Pan-African orogeny and testifies to different P-T path segments. Tourmaline inclusions in various porphyroblasts were formed during the prograde phase of metamorphism; acicular to prismatic crystals in the matrix, oriented sub-parallel to, and enveloped by, the main foliation crystallized syntectonically under prograde and peak metamorphic conditions; tourmaline cross-cutting the main foliation may have formed just after the peak or during the retrograde phase of metamorphism. Some of the cores in tourmaline crystals, showing different colours, are interpreted as former detrital grains. The abundance of tourmaline decreases with increasing peak metamorphic conditions. The tourmaline investigated belongs to the schorl-dravitess group, generally with XMg of 0.42–0.73 and XCa = Ca/(Ca+Na+K+□) of 0.02–0.24, typical of tourmalines in metapelites and metapsammites; whereas detrital cores have been derived from various sources, including former tourmaline-quartz and pre-existing high-metamorphic rocks. Tourmaline of the Sinai metasediments was formed during metamorphism of the sedimentary precursors, essentially in a closed system, where clay minerals and organic matter, together with detrital tourmaline, served as the source of boron. Although a metamorphic facies should be defined by characteristic mineral assemblages present in metamorphic rocks, tourmaline chemistry is a good monitor of P-T conditions in the metapelites and semi-metapelites investigated, showing an increase in XMg with increasing metamorphic grade, where XturMg = 0.60 distinguishes between greenschist and lower-amphibolite facies, while XturMg = 0.65 could distinguish lower- from middle- to upper-amphibolite facies. The results of tourmaline-biotite geothermometry compare well with our former temperature estimates using conventional geothermometry and phase-diagram modelling.

Micas of the muscovite–lepidolite series are main constituents of the evolved pegmatites from the Okatjimukuju-Kaliombo portion of the Karibib belt, Namibia. The compositional variations shown by the micas from the intermediate zones are mainly controlled by the Li3Al-1□-2 and SiLi2Al-2□-1 substitution schemes, whereas for the micas from the core margins and the replacement bodies, only the first of these two exchange vectors seems to operate. The chemical composition of the micas not only depends on the degree of pegmatite evolution, but also on the position in the internal zonation of the pegmatite. Micas from the core margins and the replacement units are generally richer in F, Li, Rb, Cs and Zn than those from the intermediate zones. In general, the contents of these elements increase with decreasing K/Rb ratio. However, some data departing from this general trend are also observed, which could be related to subsolidus processes. Some pegmatite bodies show a complete internal evolution, developed from the margins to the core zone, which is reflected in the chemical composition of the micas. The regional distribution of pegmatites does not define a zonation, because an overlapping of pegmatites with different degrees of evolution occurs. This could be due to the high level of evolution attained by most of the rare-element pegmatites, and to their topography with respect to a dome structure of the basement.

Two types of carbonatic cumulate xenoliths occur in alkali basalts of the northern part of the Carpatho-Pannonian region, Central Europe. One is dominated by Ca-Fe-Mg carbonates with randomly distributed bisulphide globules (Fe1+xS2, x = 0–0.1), Mg-Al spinel, augite, rhönite, Ni-Co-rich chalcopyrite, and a Fe(Ni,Fe)2S4 phase. The second, carbonatic pyroxenite xenolith type, is composed of diopside, subordinate fluorapatite, interstitial Fe-Mg carbonates, and accessory K-pargasite, F-Al-rich ferroan phlogopite, Mg-Al spinel, albite and K-feldspar. All accessory minerals occur in ultrapotassic dacite-trachydacite glass in primary silicate melt inclusions in diopside, together with calcio-carbonatite and CO2-N2-CO inclusions. Textural evidence is provided for multiphase fluid-melt immiscibility in both xenolith types. The carbonatic pyroxenite type is inferred to have accumulated from differentiated, volatile-rich, ultrapotassic magma derived by a very low-degree partial melting of strongly metasomatized mantle. Mineral indicators point to a genetic link between the carbonatite xenolith with olivine-fractionated, silica-undersaturated alkalic basalt ponded at the mantle-crust boundary.

Small (m-scale) peridotite enclaves at Planany (central Czech Republic) are separated from their gneissic host rocks by a narrow (cm-scale) reaction rim comprising an inner, tremolite + phlogopite zone and an outer, essentially monomineralic phlogopite zone. Both retain an Mg# very similar to that of the peridotite (Mg# = 81), but relative to this reference frame, show large increases in LILE (K, Rb, Ba) and radionuclides (U, Th). On a smaller scale, however, there has been a mineralogically-controlled decoupling of various components, particularly among the HFSE and REE, the former favouring the phlogopite-rich outer layer of the reaction rim, the latter the amphibole-rich inner zone. Taken together, however, the reaction zones preserve key compositional features of their inferred protolith.

Three natural amphibole samples collected from the former vermiculite mine near Libby, Montana. USA, have been analysed by Rietveld X-ray powder diffraction (XRPD) refinement and Fourier transform infrared spectroscopy (FTIR) in the OH-stretching region. The same materials have been analysed previously by electron microprobe analysis (EMPA), Mössbauer spectroscopy and structure refinement (SREF) single crystal X-ray diffraction (SC-XRD), which revealed that these amphiboles have a crystal chemical formula very close to an intermediate composition between winchite and richterite, i.e. AA0.5BNaCaCMg4.5M3+T0.5Si8O22(OH)2 (A = Na and/or K; M3+ = Fe3+ and/or Al). The Rietveld analysis showed the powder samples used for the experiments here to be composed only of amphibole. This in turn allowed us to use FTIR OH-stretching data to derive cation ordering on these powder samples. The three FTIR spectra are quite similar and up to four components can be fitted to the patterns. The two lower-frequency components (labelled A and B) can be attributed to a local O(3)-H dipole surrounded by M(1)M(3)Mg3 and M(1)M(3)Mg2Fe2+; (respectively), an empty A site and rSi8 environments; on the contrary, the higher-frequency C and D bands indicate the presence of an occupied A site. The FTIR OH-stretching data alone allow us to calculate the site occupancy of the A, M(1)–M(3) and T sites with confidence, as compared with previously published data. By contrast M(4)- and M(2)-site occupancies are more difficult to evaluate. This study takes advantage of the large database of well characterized synthetic amphiboles, built over the last two decades. The comparison of vibrational spectroscopy data with micro-chemical and crystallographic data reported in this study demonstrate that the FTIR OH-stretching method alone is a valuable and rapid method to derive or at least sensibly constrain site occupancy for natural amphiboles. A much more detailed cation site occupancy can be obtained by combining micro-chemical and FTIR OH-stretching data.

The high-pressure behaviour of manganese carbonate was investigated by in situ synchrotron X-ray powder diffraction up to 54 GPa with a laser-heated diamond anvil cell. A phase transition from rhodochrosite to a new structure form was observed at 50 GPa after laser heating. The diffraction pattern of the new high-pressure form was reasonably indexed with an orthorhombic unit-cell with a = 5.361 A, b = 8.591 A and c = 9.743 Å. The pressure-induced phase transition implies a unit-cell volume reduction of ∼5%. This result does not support the direct formation of diamond by dissociation of solid state MnCO3 reported in a previous study. Fitting the compression data of rhodochrosite to a second-order Birch-Murnaghan equation of state (Ko’ = 4) gives K0 = 126(±10) GPa. The c axis of the unit-cell parameter was more compressive than the a axis.