The Rockeskyll complex in the north, central part of the Quaternary West Eifel volcanic field encapsulates an association of carbonatite, nephelinite and phonolite. The volcanic complex is dominated by three eruptive centres, which are distinct in their magma chemistry and their mode of emplacement. The Auf Dickel diatreme forms one centre and has erupted the only known carbonatite in the West Eifel, along with a broad range of alkaline rock types. Extrusive carbonatitic volcanism is represented by spheroidal autoliths, which preserve an equilibrium assemblage. The diatreme has also erupted xenoliths of calcite-bearing feldspathoidal syenite, phonolite and sanidine and clinopyroxene megacrysts, which are interpreted as fragments of a sub-volcanic complex. The carbonate phase of volcanism has several manifestations; extrusive lapilli, recrystallized ashes and calcite-bearing syenites, fragmented during diatreme emplacement.

A petrogenetic link between carbonatites and alkali mafic magmas is confirmed from Sr and Nd isotope systematics, and an upper mantle origin for the felsic rocks is suggested. The chemistry and mineralogy of mantle xenoliths erupted throughout the West Eifel indicate enrichment in those elements incompatible in the mantle. In addition, the evidence from trace element signatures and melts trapped as glasses support interaction between depleted mantle and small volume carbonate and felsic melts. This close association between carbonate and felsic melts in the mantle is mirrored in the surface eruptives of Auf Dickel and at numerous alkaline-carbonatite provinces worldwide.

Tube-in-tube experiments involving a time-dependent variation of temperature or a strong thermal gradient were conducted in order to decipher the transport and transfer of Al in a closed medium along with dilute water. Results show that the solubility and the transport of Al are controlled by the alkali availability. Starting from a mixture of kyanite + quartz + muscovite at the hot end of a thermal gradient, Al is transported toward the cold end in the form of a complex with an Al/K stoichiometry close to unity. Since more Al than alkali are released by the dissolution of muscovite, an Al-rich phase (kyanite) forms in the vicinity of the starting minerals undergoing dissolution, although Al is mobile in the system. Then, the variation of the solubility of the Al-K complex with temperature leads to the formation of muscovite (+quartz) at the cold end of the thermal gradient. A quantitative interpretation of the experimental results was carried out using data from the literature on Al speciation in dilute water. Extrapolation of the laboratory data to natural rocks suggests that the diffusion of Al is an efficient transport process under medium-grade, low- to medium-pressure conditions. Therefore, mass-transfer estimates based on mass-balance analyses postulating a fixed Al reference frame should be considered with caution. Also the high fluid to rock ratio calculated from the amount of aluminosilicates occurring in veins of medium-grade metapelites is questionable because such calculations neglect the importance of the transport of Al by diffusion.

A specimen of zirconolite, collected from the type locality of the mineral originally described as zirkelite at Jacupiranga, São Paulo, Brazil has been re-examined and its mineral chemistry more completely characterized. All crystals studied are metamict and display very fine lamellar oscillatory zoning (1–3 µm in width) superimposed on a sector zonation. Such zoning, observed in backscattered electron images, is primarily related to differences in the concentration of Th.

In comparison with other reported zirconolite samples from a variety of geological occurrences, Jacupiranga zirconolite has higher Ca, Th, (Nb + Ta) and lower Ti and REE, which is consistent with its occurrence in carbonatitic rocks. The compositional variation with respect to an ideal zirconolite is described by two main coupled substitutions:

Calzirtite, Ca2Zr5Ti2O16, although intergrown with zirconolite and with identical major components, shows much less compositional variability with only minor amounts of Nb and Ta substituting for Ti. Unlike zirconolite, the REE and actinide elements are not easily accommodated in the calzirtite structure.

The crystal chemistry characteristics of a hydroxyl-fluor apatite from a recently discovered kalsilite-bearing leucitite from Abruzzi, Italy, were investigated by electron microprobe, single crystal X-ray diffraction, IR, Raman and micro-Raman spectroscopy. The apatite has exceptionally high S and relatively high Si, Sr and LREE, whereas the HREE content is negligible. The IR spectra confirm the presence of OH calculated from formula difference. A high positive correlation between Ca-site Substitution Index (CSI = 100(10-Ca)/Ca) and Tetrahedral Substitution Index (TSI = 100 (Si+C+S)/P atom/a.p.f.u.) and a systematic parallel increase in REE, S and Si indicate two substitution mechanisms, i.e. REE3+ + Si4+ = Ca2+ + P5+ and Si4+ + S6+ = 2 P5+. Site occupancy data and bond lengths, determined from structural refinements on selected samples, demonstrate that LREE and Sr show a marked preference for the Ca2 site, even though in the LREE-rich samples a partial substitution of LREE for Ca in the Cal site was observed.

Tetrahedral distances (from 1.535 to 1.541 Å.) reflect the substitution of Si4+ and S6+ for P5+, which is also confirmed by vibrational spectra. As (SiO4)4− and (SO4)2− substitute for (PO4)3−, the relative intensity of v1 Raman bands of (SO4)2− (at 1007 cm−1) and (SiO4)4− (at 865 cm−1) increase systematically, while that of phosphate decreases and the five components of phosphate v3 modes disappear. Moreover, the (PO4)3− Raman peak broadening is linearly correlated with the Si and S concentrations.

Apatite crystals are sometimes zoned with compositions varying from SiO2 = 1.15–2.07 wt.%, Σ(LREE2O3) = 0.56–1.08 wt.% and SrO = 0.58–1.02 wt.% in the core to 3.98–5.03, 4.14–6.73 and 1.97–2.17, respectively, in the rim. A sharp, strong enrichment in Sr and LREE in the rim indicate that the apatite suddenly became an acceptor of these elements in the late stages of crystallization.

We have performed O self-diffusion experiments in synthetic diopside single crystals along the b-axis at temperatures ranging from 1473–1643 K, under controlled O partial pressure (10−11–10−2 atm). The 18O tracer diffusion was imposed by solid/gas exchange between 16O in diopside and 18O2-enriched argon-hydrogen-H2O gas mixture. Diffusion profiles of 18O were measured by Nuclear Reaction Analysis 18O (p,α) 15N. The diffusion coefficients are described by , with log D0(m2/s)=−9.2 ± 1.0 and E 310 ± 30 kJ/mol.

Our results are in agreement with Ryerson and McKeegan's (1994) data and Farver's (1989) data along a direction perpendicular to the c direction. Experiments performed in a wide pO2 range show that D is independent of pO2.

We observe no change in the diffusion regime up to 1643 K (i.e. 22 K prior to melting temperature). This result differs from the diffusion study of Ca in diopside by Dimanov and Ingrin (1995), where a strong enhancement of Ca mobility, attributed to an excess disorder in the Ca-sublattice, was observed above 1523 K. We conclude that O diffusion in diopside is not affected by this premelting phenomenon.

Blueschist-facies metabasite rocks from the Tavşanlı Zone of northwest Turkey have been found to contain an abundance of lawsonite displaying oscillatory zoning. Lawsonite normally adheres to the ideal composition of CaAl2[Si2O7](OH)2.H2O. In two samples from the Tavşanlı Zone, Al3+-Cr3+ substitution has occurred. The Cr3+ was probably present in the protolith as magmatic chromite, became incorporated into lawsonite during subduction, and is a metamorphic feature resulting from quantities of Cr in the protolith and local fluid conditions.

Micro-FTIR (MFTIR) measurements were carried out on the natural recrystallized quartz in Ryoke granites from Mt. Takamiyama. The recrystallized quartz always shows a very strong IR absorption band at 3596 cm–1 (2.10 abs. cm–1 (normalized absorbance) under unpolarized conditions at room temperature). However, naturally deformed quartz does not show this absorption band, but only a characteristic broad band centred at 3400 cm–1. This shows that the predominant forms of H-related species in the recrystallized quartz are different from those in naturally deformed quartz. The 3596 cm–1 band is not affected by room-temperature X-ray irradiation or by annealing at temperatures of up to 600°C, and shows broadening and a positive peak shift with temperature in in situ high temperature measurements. Polarized-MFTIR measurement shows that the band has a strong polarization; the OH dipole is oriented at 35° to the a-axis in the plane and is isotropically distributed in the (0001) plane. From the stability of the band at high temperatures and against irradiation and its sharpness, the band is considered to be due to the Al(H) type point defect with no alkali which might occupy a structural position in the quartz structure.

Alkaline lamprophyre intrusives from the western Deccan Traps (Murud-Janjira, south of Bombay) host rare lithospheric xenoliths and megacrysts. The xenolith suite consists of clinopyroxenites and granulites which show eclogitic affinities. The former have transitional (porphyroclastic to equigranular) textures whereas the latter are porphyroclastic, xenomorphic to meta-igneous. The textural features provide evidence of ductile-brittle deformation. The protoliths of the pyroxenite and granulite xenoliths were formed as cumulates of alkaline and sub-alkaline magmas respectively.

Mineral chemistry and geochemical data for the xenoliths bear testimony to the metasomatized nature of the deep crust. The xenolith data coupled with the geophysical evidence indicate that the lower crust beneath Murud-Janjira is dominated by mafic granulites and pyroxenites. The latter have under- and intra-plated the continental crust beneath the region.

Experimental brackets (300–450°C) on Sb-Bi partitioning between stibnite-bismuthinites (Sb,Bi)2S3 and sulfosalts in the AgSbS2–AgBiS2 binary subsystem (α-Ag(Sb,Bi)S2, β-Ag5(Sb,Bi)4I(Sb,Bi)IIS10) and extant constraints are used to define mixing properties and standard state Gibbs energies of Sb-Bi exchange reactions. They are also used to construct a phase diagram for Ag(Sb,Bi)S2 sulfosalts. We infer that the non-ideality associated with Sb-Bi mixing is largest in minerals of the β-Ag5(Sb,Bi)4I(Sb,Bi)IIS10 series, and is sufficient to produce miscibility gaps between an ordered intermediate species Ag5(Sb)4I(Bi)IIS10 and Sb- and Bi-end-members at T < 240°C (measured in terms of symmetric regular-solution-type parameters ¼WBi−SbIβ = WBi−SbIIβ ∼ 8.5 kJ/gfw). The non-ideality associated with the Sb-Bi substitution in stibnite-bismuthinite and α-Ag(Sb,Bi)S2 is ≈ 70% that in the Ag5(Sb,Bi)4I(Sb,Bi)IIS10 series (WBi−SbBS ≈ 12.0 kJ/gfw; WBi−Sbα ≈ 6.0 kJ/gfw). It is insufficient to produce exsolution at temperatures of ore deposition (T > Tc ≈ 88°C), but most likely is responsible for a preponderance in molar Sb/Bi ratios towards end-member compositions. Finally, positive Gibbs energies of the Sb-Bi exchange reactions and indicate that Bi is more compatible in stibnite-bismuthinite sulfides than in Ag(Sb,Bi)S2 sulfosalts.

Bariosincosite is a new barium vanadium phosphate hydrate from the Spring Creek Mine, near Wilmington, South Australia. The new mineral occurs as irregular clusters of pale green, very thin platey crystals up to 250 µm across and 2 to 5 µm thick. The tetragonal crystals are tabular on {001} and the other form present is {100}. Associated with bariosincosite are quartz, cuprite, native copper, fluorapatite, whitlockite, baryte and springcreekite, BaV33+ (PO4)2(OH,H2O)6. Bariosincosite appears to have formed under supergene or low-temperature late-stage hydrothermal conditions. Electron microprobe analysis yielded: BaO 23.20; SrO 4.19; CaO 0.36; VO2 31.55; Fe2O3 0.20; Al2O3 0.50; P2O5 28.15; H2O 13.93 (calculated). These data give an empirical formula of (Ba0.77Sr0.20Ca0.03)∑1.00[(V0.964+ Al0.03Fe0.013+)∑1.00O(PO4)]2·4H2O, calculated on the basis of two P atoms. The simplified formula is Ba(V4+OPO4)2·4H2O. The mineral is transparent with a very pale green streak, a vitreous lustre and an estimated Mohs hardness of 3. The strongest lines in the X-ray powder pattern are [dobs (Iobs) (hkl)] 6.414 (20) (110, 002); 5.748 (70) (111); 4.552 (30) (112, 200); 3.198 (20) (220, 004); 3.100 (100) (203, 221); 2.847 (40) (222, 114); 2.786 (80) (311); 2.368 (30) (313, 115); and 2.017 (100) (420, 332, 116). These data were indexed on a tetragonal cell, with a = 9.031(6), c = 12.755(8) Å and V = 1040(1) Å3; the space group is probably P4/n or P4/nmm. For Z = 4 and using the empirical formula, the calculated density is 3.306 gm/cm3. Bariosincosite is uniaxial negative with ω = 1.721(2) and ε = 1.715(2) (white light); pleochroism is weak from colourless (E) to pale green (O), absorption O > E. The mineral is named for the relationship to sincosite, Ca(V4+OPO4)2·4H2O.

At Mamandur, southern India, zincian spinel is associated with Zn-Pb-Cu sulphide ores, metamorphosed to the granulite facies. The Zn-spinel (XZn = 0.44–0.82) occurs in assemblages of: (a) cordierite + biotite + sillimanite + sphalerite + pyrite and/or pyrrhotite; (b) garnet + biotite + sphalerite + pyrite and/or pyrrhotite; (c) hornblende + biotite + sphalerite + pyrite and/or pyrrhotite; and (d) it also occurs in highly sheared quartz veins with sphalerite + pyrite/pyrrhotite. Two texturally and compositionally distinct modes of occurrence of Zn-spinel have been recorded from the metamorphic assemblages: one shows a polygonal, granular (equilibrium) fabric with Zn-spinel grains in textural equilibrium with cordierite in the granulite facies assemblage; the other which is involved in the formation of coronas in garnet- and hornblende-bearing assemblage of a younger paragenesis (presumably belonging to a late retrograde stage), shows distinct compositional zoning with depletion of Zn and enrichment in Fe and Mg from the rim inwards. A third mode of occurrence is as perfectly euhedral grains embedded in a quartzose matrix in quartz veins, often with sphalerite moulded over the Zn-spinel grains.

From textural evidence and consideration of stoichiometric balance, Zn-spinel occurring in association with cordierite is suggested to have formed by the prograde reactions: 0.46 biotite (Mg-rich) + 1.80 sillimanite + 3.01 quartz + 0.11 sphalerite = cordierite + 0.20 Zn-spinel + 0.80 K-feldspar + 0.06 pyrite + 4(OH,F) or 0.48 biotite (Mg-rich) + 2.08 sillimanite + 2.72 quartz + 0.26 sphalerite = cordierite + 0.50 Zn-spinel + 0.83 K-feldspar + 0.13 S2 + 4(OH,F) and, the Zn-spinels occurring in association with garnet and hornblende by the retrograde reactions: garnet + 4.53 Al2SiO5 + 4.17 sphalerite = 5.38 Zn (-Fe)-spinel + 0.22 Ca-feldspar + 0.92 pyrite + 7.06 quartz + 1.23 S2 and hornblende + 26.93 Al2SiO5 + 20.17 sphalerite + 0.88 pyrite = 25.93 Zn-spinel + 2 Ca-feldspar + 56.81 quartz + 11.32 S2 + 2(OH,F) Zn-spinel in the sheared quartz vein may be of (meta-) hydrothermal origin. Formation of sphalerite through sulphurization of gahnite is ruled out on the evidence of the perfectly euhedral nature of the spinel and the absence of any breakdown product from the spinel.

Sideronatrite [Na2Fe(SO4)2(OH)·3H2O] occurs as yellow botryoidal encrustations on low cliffs of weathered pyrite-bearing mudstones at Barton-on-Sea, Hampshire, England. Extensive areas of the cliffs, up to ∼100 m2, are coated with sideronatrite and its low solubility in cold water secures its longevity. Dry samples of sideronatrite convert readily to metasideronatrite [Na2Fe(SO4)2(OH)·H2O], the reaction to sideronatrite being reversible. Sideronatrite, it is suggested, forms as a result of weathering of pyrite that is present in the argillaceous sediments and reaction with Na from the sea-salt spray.

The names ‘coutinite’ [= lanthanite-(Nd)], ‘coutinhite’ [= lanthanite-(La)], and ‘neodymite' [= lanthanite-(Nd) or lanthanite-(La)], do not follow the rules of nomenclature for rare earth minerals. These names were introduced without International Mineralogical Association (IMA) approval and are now formally discarded (Nomenclature Proposal 98-B) by the Commission on New Minerals and Mineral Names (CNMMN) of the IMA.

Cu K-edge extended X-ray absorption fine structure (EXAFS) spectra have been obtained for two very dilute solutions of copper in hydrosulfide solutions using beamline ID26 at the ESRF. The concentrations of the solutions (4.4 ppm {69 µM} pH 9.5, 1.2 ppm {19 µM} pH 7.4) are such that the experiments illustrate that, with the advent of third generation synchrotron sources, natural systems can now be studied by EXAFS. Analysis of the data indicates an average environment for the copper of 2.3 S atoms at 2.22 Å in the pH 9.5 solution of 2.5 S atoms at 2.23 Å in the pH 7.4 solution. These results are in accord with the solubility study of Mountain and Seward (1999), who conclude that Cu(HS)2− and Cu2(HS)2S2− are the principal copper species in such solutions.