This is the first description of rare minerals found in paralavas from a recently discovered combustion metamorphic complex in the Choir–Nyalga basin, Central Mongolia. The identified minerals contain strongly variable concentrations of Si, Ti, Mg, Fe2+ and Fe3+and most commonly have compositions intermediate in a series from kuratite Ca4Fe102+Ti2O4[Si8Al4O 36] and rhönite Ca4(Mg, Fe2+)8Fe23+Ti2O4[Si6Al6O36] to low-Ti kuratite and unnamed Ti-free Fe2+-analogue of rhönite Ca4Fe82+Fe43+O4[Si8Al4O36]. The minerals crystallized in residual Si-Al-K and Si-Al-Ca-Fe immiscible melts after spinel, anorthite–bytownite, melilite, Al-clinopyroxene ± Mg-Fe olivine, together with Fe3+-bearing hercynite, Ca-rich fayalite, kirschsteinite, pyrrhotite ± native iron, wüstite, magnetite, celsian, hyalophane, Ba-orthoclase and fresnoite, but before nepheline± kalsilite, and later sulfates, carbonates, an unidentified 'X-mineral' close to Al- and Fe-rich tobermorite and goethite. Micro-Raman spectroscopy of kuratite shows five bands near 133–155 (strong), 399–401, 545–566, 684–693 (strongest) and 828–839 cm–1.

The kuratite-bearing Nyalga paralavas have bulk compositions with MgO/(MgO+FeO+Fe2O3), mol.% ∼0.5 and a CIPW normative ratio of Ne/(Ne+Lc) = 0.23–0.76. Minerals of the rhönite–kuratite series formed during paralava crystallization at ∼1100°C.The diversity of the paralava mineral assemblages might result from local composition variations of Ca-rich silica-undersaturated melts derived from Fe-bearing carbonate-silicate sediments which were affected by nearby coal combustion sources at reducing conditions (IW-WM-QFM buffers) and at a nearly atmospheric pressure.

The dispersion and sediment-water partitioning of Pb and Zn have been studied in the Conwy River, North Wales. Analysis included major and trace element water chemistry and concentrations of sediment-hosted Pb and Zn. In situ solution pH, Eh, temperature and conductivity were also measured. Sediments were characterized via SEM, XRD, nitric acid leaching and sequential chemical extraction to quantify metal distribution and sediment phase associations. Dissolved and sediment-bound Pb and Zn within river and estuary waters and sediments have been used to calculate whole sediment- and phase-specific apparent partition coefficients.

Weathering of galena and sphalerite, associated with the Llanrwst Mining Field, provide point sources of elevated dissolved and sedimentary Pb and Zn in the upper catchment. Dissolved Pb is actively adsorbed onto sedimentary surface coatings of Fe-Mn (hydr)oxides and organics whilst Fe-Mn (hydr)oxides, organics and carbonates were the main hosts for Zn. Systematic changes in metal sorption are evident between the estuary and the upper catchment, with organic matter becoming progressively more important upstream. This change is ascribed to the sorptive properties of sedimentary organic material. Solution pH, [Cl] and aqueous metal speciation are the dominant solution controls on metal partitioning. Laboratory sorption experiments parallel Pb sorption behaviour in the natural system.

In addition to the normal type of chromite alteration, an antipathetic form of alteration has been observed in the ultramafic zone of the Panton Sill, Western Australia. The chromites display margins of lower reflectivity related to a marked enrichment in MgO and Al2O3 and depletion in Cr2O3, Fe2O3, and FeO, such that a spinellid of composition lying between the end members MgAl2O4 and FeAlaO4 is formed. The alteration is related to the formation of secondary spinel in the ground-mass during the hornblendization of primary silicates under metasomatic conditions accompanied by low oxygen activity.

Apatite concentrates obtained from a carbonatite of the Tororo complex contain cogenetic fluid and solid primary inclusions. The solid inclusions are commonly composed of calcite and shortite and these minerals, together with the host apatite, were deposited from aqueous fluids at approximately 400°C.

Inorganic calcite precipitation experiments were conducted to determine whether inducing specific orientations of calcite crystal growth can cause the enrichment of cations larger than Ca. Malonic acid (CH2(COOH)), a di-carboxylic acid, was used to poison growth on acute kink sites, promoting growth on obtuse kink sites, causing calcite crystals elongated along their c-axes to form in a mechanism similar to that seeninthe growth of E. huxleyi coccoliths. Calcite was precipitated with a range of malonic acid concentrations (0 to 10-1 M), and 9x10-5 M of either SrCl2 or MgCl2. The results show that calcite crystals precipitated in the presence of large malonic acid concentrations show significant elongation along the c axis, and suggest that increasing malonate concentrations corresponded with increasing DSr. Experiments with 10-1 M malonic acid caused elevated DSr comparable to that predicted for E. huxleyi coccolith calcite (Langer et al., 2006).

Pyrochlore-group minerals are common accessory rare-metal bearing minerals in the calcite and ankerite carbonatites of the Amba Dongar complex (India). Pyrochlore from the Amba Dongar carbonatites differs from that in other Indian complexes in Ta, Zr, Ti, rare earth element (REE) and Pb contents, but is similar with respect to Ca, Ba and Sr abundances. The evolution of pyrochlore composition was studied to understand the alteration processes and the formation of late-stage pyrochlores enriched in REE and Pb. The early magmatic pyrochlore are calcio- and niobium-dominant types and were replaced by secondary cation-deficient varieties as a consequence of the action of hydrothermal fluids and supergene weathering. These processes produce changes mainly at the A site, rarely at the B site, and the original F is replaced by OH– groups. Calcium and Na can be extracted from the structure at the alteration stage and charge balance is achieved by the introduction of REE, Th, U, Ba or Sr. At the latest supergene stages, marginal and fractured zones of pyrochlore grains are altered to Pb-rich, Si-rich and cation-deficient hydrated varieties. The magmatic pyrochlore was crystallised in a highly alkaline environment at a high activity of Ca and at temperatures near 600°C, the alteration of pyrochlore began in a hydrothermal environment at temperatures below 350°C. The major compositional changes that are associated with the alteration are summarised by the following reactions: Ca2+ + Nb5+→ REE3+ + Ti4+; Nb5+ + Fe3+ → Ti4+ + Zr4+; and 2Nb5+ + Ca2+ → Ti4+ + Si4+ + U4+.

Field, petrographic, and chemical data are presented which make it possible to follow the course of back-veining of felsite by a gabbro ring-dyke. The remelted felsite back-veined the chilled margin of the gabbro, then acidified the partly crystalline basic mush within the chilled zone and finally mixed with the mainly liquid basic magma farther inside the dyke to produce hybrids of marscoitic aspect. Spectrographically determined trace-element data, with data on some major elements, illustrate these changes. The veins are shown to have a composition nearer the ternary minimum in the system Ab-Or-Qz-H2O than the parent felsite, while culminations of soda and iron in the acidified gabbros and hybrids suggest that metasomatism has accompanied the mixing of the partly liquid end members. This study confirms the earlier suggestion that the gabbro post-dates the felsite.

The results of a chemical analysis of a mineral are always presented, in the first place, as percentages of elements or oxides present, and until recently the only possible further treatment of these values was to calculate atomic or molecular ratios, group them according to accepted isomorphous groups, and deduce (if possible) an integral chemical formula. The degree of approximation to integral ratios accepted as satisfactory is, of course, quite arbitrary, and a decision as to the degree of complication acceptable in a chemical fornmla has often had to rest on very inadequate evidence. Some workers prefer to adjust the final ratios to show the errors evenly distributed, a procedure which has no real advantages.

The processes by which a metal–oxygen bond dissociates in aqueous complexes are discussed and the reactions related to more complicated pathways of mineral dissolution. The dissolution of oxide minerals, and in fact many other classes of surface reactions, can be viewed as a ligand-exchange reaction because the bridging oxygens that link the metal to the mineral are progressively replaced by non-bridging functional groups. These ligand-exchange reactions are accelerated by protonations, hydroxylations and ligand substitutions that modify the lability of surface oxygens, but always at specific sites. Molecular information is important because reactions at some sites retard rates while reaction at other sites enhance them. Virtually all of the important variables that affect these reaction rates are local.

Coherent intergrowths, at the lattice scale, between cuprobismutite (N = 2) and structurally related paděraite along both major axes (15 Å and 17 Å repeats) of the two minerals are reported within skarn from Ocna de Fier, Romania. The structural subunit, DTD, 3 layers of paděraite, is involved at interfaces of the two minerals along the 15 Å repeat, as well as in transposition of 1 paděraite unit to 2 cuprobismutite units along the 17 Å repeat in slip defects. Lattice images obtained by HRTEM across intervals of 200–400 nm show short- to long-range stacking sequences of cuprobismutite and padeÏ raite ribbons. Such nanoscale slabs mimic mm-scale intergrowths observed in back-scattered electron images at three orders of magnitude greater. These slabs are compositionally equivalent to intermediaries in the cuprobismutite-paděraite range encountered during microanalysis. Hodrushite (N = 1.5) is identified in the mm-scale intergrowths, but its absence in the lattice images indicates that, in this case, formation of polysomes between structurally related phases is favoured instead of stacking disorder among cuprobismutite homologues. The tendency for short-range ordering and semi-periodic occurrence of polysomes suggests they are the result of an oscillatory chemical signal with periodicity varying from one to three repeats of 15 Å, rather than simple ‘accidents’ or irregular structural defects. Lead distribution along the polysomes is modelled as an output signal modulated by the periodicity of stacking sequences, with Pb carried within the D units of paděraite. This type of modulator acts as a patterning operator activated by chemical waves with amplitudes that encompass the chemical difference between the minerals. Conversion of the paděraite structural subunit DTD to the C unit of cuprobismutite, conserving interval width, emphasizes that polysomatic modularity also assists interference of chemical signals with opposite amplitudes. Observed coarsening of lattice-scale intergrowths up to the mm-scale implies coupling between diffusion-controlled structural modulation, and rhythmic precipitation at the skarn front during crystallization.

Trioctahedral micas in the Karlovy Vary pluton range in composition from Fe-biotites in the granites of the Older Intrusive Complex (OIC) through siderophyllite and lithian siderophyllite to zinnwaldite in the granites of the Younger Intrusive Complex (YIC). Li + AlVI + Si would appear to substitute for Fe2+ + AlIV in biotite with a formula similar to that given in Henderson et al. (1989), but Li + Si appears to substitute for Fe2+ + AlIV in the Li-micas. In mica vs. host rock plots, Rb and F show positive linear covariation except for the Li-mica granites, but femic constituents and tFeO/(tFeO + MgO) have separate trends for OIC and YIC granites and micas. Further differences between OIC and YIC granite micas are seen in their Ti and Mg contents and in plots like V vs. SiO2, AlIVvs. Fe/(Fe+Mg) and Li vs. total iron as Fe2+ and in the results of discriminant analysis. These reveal a geochemical hiatus between OIC and YIC granite micas that coincides with a major temporal hiatus.

Biotite compositions in the YIC granites are similar to those in the granites of the Cornubian batholith and reveal a similar magmatic evolution and genesis in which later biotites evolve to lithian siderophyllites with some enrichment in trace alkalis and F. It is suggested that the biotite granites in the YIC were derived from the products of partial fusion of the OIC granites. A less well-marked geochemical hiatus exists between YIC biotites and zinnwaldites. In some plots (e.g. Si vs. Li, Li vs. tFe) apparent continuity between biotite and the Li-micas suggests continuous evolution, but in others (e.g. Rb vs. TiO2, Rb(biotite) vs. Rb(rock)), Li-mica data points stand apart from the biotites suggesting, like the whole rock data, a separate evolution. Comparison with the more abundant data for Li-micas of the Cornubian batholith suggests derivation of the Li-mica granites by partial fusion of the OIC/YIC granite residues.

Kidwellite, NaFe93+(OH)10(PO4)6·5H2O, monoclinic, Z = 2, a = 20·61(7) Å, b = 5·15(1) Å, c = 13·75(6) Å, β = 112·64(15)·, space group A2/m, Am, or A2, is a new species that occurs in moderate abundance as a late-stage mineral associated with rockbridgeite, dufrenite, beraunite, and strengite in novaculite deposits. Colour lively pale chartreuse-green, to greenish-yellow, greenish-white, and bright yellow. H = 3, lustre silky, streak yellow, cleavage {100} perfect, habit acicular elongated parallel to [010], flattened on {100}, biaxial (−), α = 1·787(5), β = 1·800(5), γ = 1·805(5), 2V large, β∥b, not discernibly pleochroic.

The mineral is moderately widespread as a replacement of rockbridgeite and beraunite from the Ouachita Mountains, Arkansas; Indian Mountain, Alabama; Irish Creek, Virginia; Waldgirmes, West Germany. A related, but apparently distinct, species is also noted from the McMahon pegmatite, South Australia, and the Sapucaia pegmatite, Minas Gerais, Brazil.

Melt generation during granulite-grade metamorphism is believed to be controlled by the stability temperatures of biotite, whose breakdown provides H2O and controls fluid-absent melting in the lower crust. In a simple KMASH system, the restite minerals crystallising due to incongruent melting of phlogopite depend upon the bulk composition. In an alumina-poor and silica-rich portion of the system (Phl + Qtz), enstatite appears with the melt, while in an alumina-rich system (Phl + Sil + Qtz) cordierite appears first instead of enstatite. Since the temperature of biotite stability is believed to be strongly controlled by its F and Ti content, it will have significant effect on the fluid-absent melting reactions during granulite-grade metamorphism of mica-containing granites as well as pelitic rocks in the deeper crust.

To understand such effects in an aluminous portion of the KMASH system, experiments were performed (between 850 and 1100°C and at 7, 10 and 12 kbar) with bulk composition containing 2Phl-6Sil- 9Qtz, where natural phlogopite with F/(F+OH) = 0.39 and Mg/(Mg+Fe) = 0.96 was used. In runs with this charge and containing 5 wt.% of excess water, cordierite appeared around 920°C at 7 kbar and 990°C at 12 kbar, and it disappeared at about 1080°C with the appearance of 221 sapphirine. In fluid-absent runs, these boundaries marginally shift to higher temperatures (30-50°C). The enstatite which was distinctly absent in H2O-saturated runs, crystallises in the high-temperature sapphirine field with up to 12 wt.% Al2O3 in H2O-undersaturated runs. The enstatite formation with cordierite is perhaps inhibited due to the Al consumption by cordierite and instability of Al-free enstatite at temperatures of cordierite stability. Re-equilibrated phlogopite persists in both the cordierite and sapphirine fields. The temperatures of the beginning of phlogopite breakdown are about 100-140°C above those reported for reaction Phl + Qtz → En + Sa + L (Vielzeuf and Clemens, 1992) with F and Ti-free phlogopite, but are ≈50–100°C lower than the temperatures reported (Tareen et al., 1995; Dooley and Patino Douce, 1996) for the same reaction containing F- and Ti- bearing phlogopite. The combined effect of the F and Ti content in phlogopite on its stability temperatures in the KMASH system has been found to be additive in relation to those containing only F or Ti. H2O-saturated runs produced per-aluminous melts with ≈27 wt.% Al2O3 in the cordierite field and ≈23% Al2O3 in the sapphirine field. The H2O-undersaturated runs produced melts rich in K2O (≈10 wt.%), SiO2 (72.5 wt.%) and relatively poor Al2O3 (12 wt.%).

The chlorite data presented are from four igneous complexes covering the compositional spectrum of igneous rocks (gabbro to granite) of orogenic and anorogenic settings. The four igneous complexes are; early orogenic gabbro-diorite-tonalite (D-T) suite, late orogenic granodiorite-adamellite (G-A) suite (both are calc-alkaline suites), high-alumina trondhjemite (TR), and anorogenic peralkaline granite (PGR).

Chlorites in these igneous rocks show characteristic compositional fields. The Mg vs Fe plot provides the best discriminant, as data points define three compositionally different groups. Phases in the PGR are Fe-rich, siliceous, interlayered chlorite-smectite (Fe/Mg = 8.6), and differ significantly from those in the calc-alkaline D-T and G-A rocks which are Mg-rich chlorites (Fe/Mg = 0.6–0.8). The X-ray diffraction data for the peralkaline granite samples show superlattice reflections at approximately 31 Å (air-dried) and 34 Å (ethylene glycollated), thus suggesting the presence of an expandable (smectite-like) component in this interlayered (chlorite-smectite) phyllosilicate phase. Chlorites in the peraluminous TR rocks contain Fe/Mg values intermediate between the other two types (Fe/Mg = 1.3). Tetrahedral Al (AlZ) values are remarkably low (0–0.5) in phyllosilicates in the PGR, but vary from 1.9–2.5 in chlorites from the other suites. Yet, these chlorite groups with their generally low AlZ values are distinct from the more stable (type IIb) metamorphic chlorites. Sedimentary chlorites are somewhat similar, in their low AlZ values and metastable structural type, to chlorites in igneous rocks.

In the calc-alkaline rocks, chlorite may have been formed at the expense of both biotite [biotite + 3M + 3H2O = chlorite + A], and calcic amphibole [2 Ca-amphibole + 6H2O + 5O2 + 1.8Al = 1 chlorite + 8SiO2 + A], where M = Fe, Mg, Al, and A = K, Na, Ca. The alteration of alkali amphibole in the peralkaline rocks may have produced interlayered chlorite-smectite via this reaction; [1 Na-amphibole + 7H2O + 2.5O2 + M = 1 chlorite-smectite + A]. The presence of such interlayered chlorite-smectite which typically form at low T (150–200°C) suggests that the region was not affected by any major reheating events, which is consistent with the nature of the feldspars.

Feinglosite, the zinc analogue of arsenbrackebuschite, was found lining a cavity in a sample of massive chalcocite from Tsumeb, Namibia. In this cavity it is associated with wulfenite, anglesite and goethite. The mean of seven electron-microprobe analyses (wt.%) is: PbO 61.4, ZnO 7.3, FeO 1.8, As2O5 22.1, SO3 5.3, H2O (by difference) [2.1], total = [100.00]%, leading to the ideal formula: Pb2(Zn,Fe)[(As,S)O4]·H2O. Feinglosite is monoclinic, space group P21 or P21/m, a 8.973(6), b 5.955(3), c 7.766(6) Å, β 112.20(6)°, with Z = 2. The strongest five reflections of the X-ray powder diffraction pattern are [d in Å (I) (hkl)]: 4.85 (50) (110), 3.246 (100) (112), 2.988 (60) (301), 2.769 (60) (300/211), 2.107 (50) (321). The mineral is pale olive-green, transparent, sectile, and has a white streak and adamantine lustre. It overgrows clusters of goethite crystals and forms globular microcrystalline aggregates up to 0.5–0.75mm in size. The hardness on Mohs' scale is 4–5: the mean micro-indentation hardness is 263 at VHN100. Its calculated density is 6.52 g cm−3. The mineral is pale brownish grey in reflected light (when compared with goethite). Visible spectrum reflectance data are presented. Feinglosite is named for Mark N. Feinglos who first recognised the mineral on a specimen in his collection.

Widespread secondary andradite-grossular-hydrogrossular garnet, epidote, prehnite and titanite occur throughout the Galway Granite and its satellite plutons (Roundstone; Inish; Omey and Letterfrack) and even in some of the country rocks several kilometres from the granites. These minerals are not found in low CaO (<1%) granites. They formed as result of secondary fluid movements which altered the biotite, plagioclase and hornblende and also produced sericite and chlorite.

The rare barium zeolite edingtonite has been examined in the course of the systematic investigation of the zeolites now being made at the British Museum, and several substitution derivatives have been prepared. The structure of natural edingtonite has also been completely determined by X-ray methods, and in the present paper an account is given of an attempt to discover the exact positions occupied in the substituted edingtonites by the potassium and thallium ions which replace the barium ions of ordinary edingtonite.

Base-exchange products obtained from some other zeolites have already been examined in detail by X-ray methods. In silveranalcime and silver-natrolite the intensities of X-ray reflections are explained satisfactorily on the assumption that each silver ion occupies the exact position previously occupied by the sodium ion which it replaces.