Anorthite megacrysts are common in basalts from the Japanese Island Arc, and signally rare in other global fields. These anorthites are 1 to 3 cm in size and often contain several corroded Mg-olivine inclusions. The megacrysts generally range from An94Ab4Ot2 to An89Ab6Ot5 (Ot: other minor end-members, including CaFeSi3O8, CaMgSi3O8, AlAl3SiO8, □Si4O8) and show no chemical zoning. They often show parting. Redclouded megacrysts contain microcrystals of native copper with a distribution reminiscent of the shape of a planetary nebula. Hydrocarbons are also present, both in the anorthite megacrysts and in the olivines included within them. Implications of lateral variations in the Fe/Mg ratio of the included olivines, in Sr-content and in Sr-isotope ratio of the anorthite megacrysts with respect to the Japanese island arc, relate to mixing of crustal components and subducted slab-sediments into the basaltic magmas.

Hydrogen in H-feldspar obtained by ion-exchange was studied in the spectral range 1000–5500 cm−1 by single crystal IR microspectroscopy. Spectra were almost identical for H-feldspars prepared either from sanidine or from adularia. Two bands in the middle-infrared were identified by D/H exchange as OH vibration modes. One broad band with a maximum at 3000 cm−1 and shoulders at 2800, 3200 and 3500 cm−1 confirms previous work. An additional OH absorption band with a maximum at 2485 cm−1 was observed for the first time in feldspars. The pleochroism of the OH absorption bands suggests that the H-feldspar is composed of two phases, an amorphous phase and a feldspathic phase. The proportion of the amorphous phase is increased by heating, producing a shift of the maximum of the band at 3000 cm−1 towards higher wavenumber and a decrease of the intensity of the band at 2485 cm−1. Near-infrared spectroscopy showed that hydrogen is present as hydroxyl groups bound to tetrahedral cations in both phases. Molecular water was not detected. The experimental results imply that hydrogen is incorporated in the H-feldspars as protons attached to bridging oxygen as well as to non-bridging oxygen. The complex structure of the IR spectra implies that the protons are distributed over a large number of sites in the cation cavity of the feldspars.

High-temperature Raman spectroscopy and optical microscopic observations have revealed a new metastable polymorph of CaAl2Si2O8 composition, which brings to four the number of known crystalline phases in this system. Similar to the metastable monoclinic pseudo-orthorhombic and pseudo-hexagonal phases, the new polymorph nucleates prior to anorthite, at around 1545 K, and its pseudo-liquidus temperature is 1700 ± 10 K. It can also be formed from the transformation of the pseudo-hexagonal phase at 1050 K. The actual structure of this new crystalline form is unknown, but its Raman spectrum indicates that it is most likely a 6-membered alumino-silicate framework. We have obtained all three metastable phases as pure single crystals using wire loop heating techniques, and have studied their structures via Raman spectroscopy up to their metastable melting points or transformation temperatures.

At Alijó-Sanfins there are many granitic aplite and pegmatite veins crosscutting different petrographic facies of the Hercynian granite batholith and also mica-schists. They are tin-bearing granitic rocks. Thirty-four samples of K-feldspar and 34 of albite from these veins and host granites were analysed to establish the distribution of elements and their fractionation trends in the sequence of feldspar crystallization. Rubidium and Cs increase, and Ba, Sr, Ba/K, Sr/K and K/Rb decrease in K-feldspar, whereas Na increases and Sr and Ca decrease in albite, from granites to aplites and pegmatites. In a few aplite-pegmatite veins Rb, Rb/Ba and Rb/Sr increase and Ba, Sr, K/Rb and Ba/Sr decrease in K-feldspar, and Rb increases and Sr decreases in albite from aplite to coexisting pegmatite. Equilibrium was not attained for trace elements between coexisting feldspars.

This paper presents a 27Al and 29Si MAS NMR study of K-feldspars and demonstrates that the spectra are sensitive to variations in the state of Al,Si order. For synthetically annealed samples, the results are in agreement with previous IR spectroscopy (Harris et al., 1989) and demonstrate that Al,Si rearrangement continues after the samples have become monoclinic as determined by powder XRD. NMR methods provide a significantly improved picture of the state of local Al,Si order in such samples. For triclinic samples, measures of the state of Al,Si order (M1 and M2 of 27Al spectra and M2 of 29Si spectra) correlate well with site occupancies determined by powder XRD, but for the monoclinic samples the NMR parameters continue to change whereas the XRD parameters do not. Interpretations based on the NMR results for the synthetically disordered samples are consistent with 1-step disordering, as observed by XRD. 27Al and 29Si MAS NMR is likely to be a useful tool for probing the state of local Al,Si order in a wide variety of natural samples.

Alkali feldspar phenocrysts (bulk composition Or75.0Ab24.6An0.4) in the subsolvus Shap granite comprise a fine-scale mixture of subregular pristine crypto- and micro-perthites with altered, micropore-rich feldspar with irregular microstructures. The regular perthites are strain-controlled intergrowths of Albite and/or Periclinetwinned albite exsolution lamellae within tweed orthoclase. The microperthites formed at ⩽ 590°C by heterogeneous nucleation of thin albite films which coarsened to > 1 µm length. Cryptoperthites developed at < 400°C by homogeneous nucleation of sub-µm long platelets between films. Platelets are coherent, but the coarser microperthite lamellae are semi-coherent, with pairs of misfit dislocations sub-regularly spaced along the albite-orthoclase interface. As much as 30% of any one feldspar crystal is turbid, a result of the formation of numerous µm to sub-µm sized micropores during deuteric alteration. In some areas, deuteric fluids gained access to the interior of feldspar crystals by exploiting semi-coherent film lamellae. Albite was selectively dissolved and micropore-rich irregular microcline was reprecipitated in its place. In other parts of the feldspars deuteric recrystallization completely cross-cuts the pristine microtextures and patch perthites have formed. These are coarse, incoherent to semi-coherent intergrowths of irregular microcline (replacing tweed orthoclase) and Albite-twinned albite. The deuteric reactions occurred at < 400°C; the main driving force for dissolution and reprecipitation was decrease in the elastic strain energy at the coherent interfaces of crypto-and micro-perthite lamellae, and the recrystallization of tweed orthoclase to irregular microcline.

The distribution of potassium and strontium, potassium and barium between feldspars and aqueous chloride solutions was studied at 700°C, 2 kbar and 800°C, 2 kbar respectively. The distribution of Sr and Ba between coexisting feldspar and chloride solutions is not ideal; Sr and Ba are enriched in feldspar relative to solution. In order to estimate the phase state of the chloride solutions, special experiments were conducted using the synthetic fluid-inclusion method in the systems KCl-BaCl2-H2O and KCl-SrCl2-H2O at 700–800°C, 2 kbar. It was shown that (0.5M KCl+0.5M SrCl2) aqueous solution is homogeneous at 800°C, 2 kbar. The 0.25–0.5M SrCl2 solutions are homogeneous at 700°C 2, kbar. The (0.5M KCl+0.5M BaCl2) solution is homogeneous at 700°C, 2 kbar and heterogeneous at 800°C, 2 kbar. Margules parameters for describing the excess energy of mixing of the (K,Sr)- and (K,Ba)-feldspar solid solutions were calculated. The integrated values of excess energy of mixing () were estimated for the different binary feldspar solid solutions, and a correlation of with the crystallochemical parameter ρ = (RA-RB)/D(Me-O) was observed. Feldspar solid solutions can be subdivided into three groups based on the relationship between , p and the stability of the solid solution.

Talc was identified as an equilibrium associate of omphacite, kyanite, zoisite, and garnet in some coesitebearing eclogites and as a retrograde phase in associated garnet peridotite from the Bixiling mafic-ultramafic complex in the Dabie ultrahigh-P metamorphic terrane, central China. Observed talc- and tremolite-bearing assemblages within the coexisting mafic and ultramafic rocks together with established phase relations for the simple system CaO-MgO-Al2O3-SiO2-H2O constrain the P-T path for retrograde metamorphism. This, together with reported talc occurrences from the Dora Maira massif, leads to the conclusion that UHP talc assemblages are confined to mafic and pelitic rocks of unusual chemistry, and are not stable at ultrahigh pressures in ultramafic rocks. Thus, talc cannot be an important H2O-bearing phase in deep mantle ultramafic rocks.

We have carried out TEM observations of agates of geode origin and Beltane opals. Optically observable individual fibres in agates are composed of many fine fibres which consist of quartz crystallites of 8 to 100 nm in length stacked together parallel to <110> or <100> with c-axes perpendicular to the fibre elongation. The optically observable systematic striations in agate are found to consist of cyclic alternation of layers due to variation in grain size and porosity. Large quartz crystals, protruding into the spaces of geodes, represent the last stage of formation of these bands, and are merely a continuation of the banding sequence. Nanometre scale textures of cristobalite fibres were revealed in Beltane opals. The cristobalite crystallites have the size of 3 to 20 nm in length and are also stacked together. Our TEM results suggest that embryonic particles were formed in their corresponding growth environments and agglutinated to form fibres.

The transmittance spectra of a synthetic alexandrite recorded along directions parallel to the three crystallographic axes are generally similar, but the observed colour changes along these directions under different light sources are quite different. Calculated hue-angle changes for the colours observed under different pairs of C.I.E. standard illuminants are the largest for light travelling parallel to the a-axis. Therefore, alexandrite should be cut as a gemstone with the top facet oriented parallel to (100) for it to show the most dramatic change in colour.

Morimotoite, Ca3TiFe2+Si3O12, has been found in contaminated rocks which are considered to be a kind of endoskarn at Fuka, Bitchu-Cho, Okayama Prefecture, Japan. Morimotoite is derived from andradite, , by the substitution Ti + Fe2+ = 2Fe3+. It is associated with calcite, vesuvianite, grossular, wollastonite, hematite, prehnite, fluorapatite, perovskite, zircon, baddeleyite and calzirtite. It is cubic with space group Ia3d. The unit cell dimension a is 12.162(3) Å. Its refractive index n is 1.995(2) and the density 3.75(2) g cm−3 (meas.), 3.80 g cm−3 (calc.). The Mohs' hardness is 7.5. Calculation of the analytical data on the basis of twelve oxygen atoms and eight cations shows that this mineral has a simplified chemical formula Ca3(Ti,Fe2+Fe3+)2(Si,Fe3+)3O12 where Ti > Fe2+ > 0.5. Morimotoite was synthesized at low oxygen fugacities, 650 and 700°C and 1 kbar total pressure.

PEEM allows ‘real-time’ observations to be made of solid-state transformations and other high-temperature processes taking place during vacuum-heating up to c. 2000°C The solid state transformations of an amphibole-rich hornblendite specimen have been observed in the temperature range of 750–1000°C (± 50°C Between c. 970–990°C a rapid change in orientation contrast was observed, indicating a structural rearrangement from an oxyhornblende crystal lattice to a clinopyroxene structure. This phase retains the original amphibole shape and texture (including two 120°C intersecting cleavage traces), but possesses a clinopyroxene crystal structure. At higher temperatures this phase is seen to decompose, forming iron oxides and other fine-grained products. PEEM has provided useful information on both the nature and rates of transformation of natural amphiboles which has proved invaluable in our understanding of the mineralogically-controlled mechanisms of argon release during 40Ar/39Ar dating of amphibole samples.

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.

Kintoreite is a new lead iron phosphate mineral in the alunite-jarosite family, from Broken Hill, New South Wales, Australia. It is the phosphate analogue of segnitite and the iron analogue of plumbogummite. Kintoreite occurs as clusters and coatings of cream to yellowish green rhombohedral crystals up to 2 mm high and with the principal form {112}. The mineral also forms waxy, yellowish green globular crusts and hemispheres on other phosphate minerals. These associated species include pyromorphite, libethenite, rockbridgeite/dufrenite, apatite and goethite. Kintoreite formed during oxidation of primary ore rich in galena, in the presence of solutions with high P/(As + S) ratios. The mineral is named for the locality, the Kintore opencut, in which it is most common. A mineral closely resembling kintoreite in composition has also been found at several mines in Germany. Type material is preserved in the Museum of Victoria and the South Australian Museum.

Electron microprobe analysis showed a nearly complete spread of compositions across the P-dominant portion of the segnitite-kintoreite series. The selected type specimen has an empirical formula of Pb0.97(Fe2.95Zn0.13Cu0.02)Σ3.10[(PO4)1.30(AsO4)0.39(SO4)0.18(CO3)0.11]Σ1.98(OH)5.45·0.74H2O, calculated on the basis of 14 oxygens and with all Fe trivalent. The simplified formula is PbFe3(PO4)2(OH,H2O)6. Kintoreite crystals are translucent with a vitreous to adamantine lustre, with globules appearing waxy. The streak is pale yellowish green and the Mohs hardness is ∼ 4. Crystals show good cleavage on {001} and are brittle with a rough fracture. The calculated density is 4.34 g cm−3. Kintoreite crystals are uniaxial negative with RIs between 1.935 and 1.955 and show light yellowish green to medium yellow pleochroism.

The strongest lines in the X-ray powder pattern are (dobs, Iobs, hkl) 3.07(100) 113; 5.96(90)101; 3.67(60)110; 2.538(50)024; 2.257(50)107; 1.979(50)303; 1.831(40)220. The X-ray data were indexed on a hexagonal unit cell by analogy with beudantite, giving a = 7.325(1) Å, c = 16.900(3) Å, V = 785.3(5) Å3 and Z = 3. The probable space group is Rm, by analogy with beudantite and other members of the alunite-jarosite family. Powder X-ray diffraction data for several intermediate members suggest that the segnitite-kintoreite series may not represent ideal solid solution.

During the study of kintoreite, part of the type specimen of lusungite from Zaïre was obtained and shown to be goyazite. The IMA's Commission on New Minerals and Mineral Names has voted to discredit lusungite as a species, and has approved the renaming of the ‘lusungite’ group as the segnitite group. However, as relationships between crystal structure, order-disorder and solid solution in the Pb-rich minerals of the alunite-jarosite family are not well documented, the nomenclatural changes resulting from this study should be seen as interim only.

Crystal structure refinements were performed on five Al-rich phlogopite-1M crystals (1.50 ⩽ Al3+ ⩽ 1.97 atoms per formula unit) from skarns of the Predazzo and Monzoni Hills petrographic area (north-east Italy) with the aim of characterizing geometrical variation produced by Al3+ increase. The charge imbalance was mostly compensated for by substitutions of highly charged cations in the octahedral sheet (Al3+ and/or Fe3+ for Mg2+). The refinements were carried out in the mean space group C2/m and gave agreement values (R) between 0.025 and 0.030. For some additional crystals, only chemistry and/or unit cell parameters were determined. In all samples the tetrahedra are more regular and larger than those previously reported in the literature for phlogopite crystals and the misfit between tetrahedral and octahedral sheets, produced by the increase in the tetrahedral edges, is mostly compensated for by the tetrahedral ring angle rotation α (10.2 °⩽ α ⩽ 12.5°), whereas the octahedral sheet features seem affected only by local crystal-chemical variations.

The crystal structure of vlodavetsite, AlCa2(SO4)2F2Cl·4H2O, has been determined, space group I4/m, a = 6.870(1), c = 13.342(2) Å, Z = 2, Dx = 2.35 g/cm3. The polyhedron cation chains are parallel to [001] and consist of couples of distorted Ca octahedra alternating with one distorted Al octahedron rotated through 24° with respect to the former. The chains are linked by SO4-tetrahedra so that all of the four tetrahedron oxygen atoms take part in coordination of Ca atoms to form a distorted octahedron with Cl and F atoms. The Al coordination polyhedron consists of two F atoms and four oxygen atoms belonging to water molecules. There is a specific interaction via hydrogen bonds between oxygen atoms of SO4-tetrahedra and water molecules.