The crystal structure of new lead chloride arsenite, Pb5(As3+O3)Cl7 [orthorhombic, Pbcn, a = 16.894(2), b = 10.913 (1), c = 16.760(2) Å, V = 3090.1(7) Å3], from the historic slags of Lavrion, Greece, has been solved by direct methods and refined to R1 = 0.069. The structure contains five symmetrically unique Pb, one As, eight Cl and three O sites. The As atom forms three nearly equal As—O bonds which result in the formation of an AsO3 trigonal pyramid with As at the apex. The Pbl. Pb2, Pb3 and Pb4 atoms are bonded to the AsO3 groups via Pb2+—O bonds to form complex [Pb4(AsO3)] chains parallel to the b axis. The Pb(5) atom is coordinated solely by Cl– anions. The resulting Pb(5)Cl7 polyhedra share common edges and corners to produce bent chains parallel to the c axis. A short compilation of structural features of known lead chloride arsenites is given.

The crystal structure of the manganese phosphate mineral gatehouseite, ideally Mn52+(PO4)2(OH)4, space group P212121, a = 17.9733(18), b = 5.6916(11), c = 9.130(4) Å, V= 933.9(4) Å3, Z = 4, has been solved by direct methods and refined from single-crystal X-ray diffraction data (T = 293 K) to an R index of 3.76%. Gatehouseite is isostructural with arsenoclasite and with synthetic Mn52+(PO4)2(OH)4. The structure contains five octahedrally coordinated Mn sites, occupied by Mn plus very minor Mg with observed <Mn—O> distances from 2.163 to 2.239 Å. Two tetrahedrally coordinated P sites, occupied by P, Si and As, have <P—O> distances of 1.559 and 1.558 Å. The structure comprises two types of building unit. A strip of edge-sharing Mn(O,OH)6 octahedra, alternately one and two octahedra wide, extends along [010]. Chains of edge- and corner-shared Mn(O,OH)6 octahedra coupled by PO4 tetrahedra extend along [010]. By sharing octahedron and tetrahedron corners, these two units form a dense three-dimensional framework, which is further strengthened by weak hydrogen bonding. Chemical analyses by electron microprobe gave a unit formula of (Mn4.99Mg0.02)Σ5.01(P1.76Si0.07(As0.07)Σ2.03O8(OH)3.97.

The significance of the potential impacts of microbial activity on the transport properties of host rocks for geological repositories is an area of active research. Most recent work has focused on granitic environments. This paper describes pilot studies investigating changes in transport properties that are produced by microbial activity in sedimentary rock environments in northern Japan. For the first time, these short experiments (39 days maximum) have shown that the denitrifying bacteria, Pseudomonas denitrificans, can survive and thrive when injected into flow-through column experiments containing fractured diatomaceous mudstone and synthetic groundwater under pressurized conditions. Although there were few significant changes in the fluid chemistry, changes in the permeability of the biotic column, which can be explained by the observed biofilm formation, were quantitatively monitored. These same methodologies could also be adapted to obtain information from cores originating from a variety of geological environments including oil reservoirs, aquifers and toxic waste disposal sites to provide an understanding of the impact of microbial activity on the transport of a range of solutes, such as groundwater contaminants and gases (e.g. injected carbon dioxide).

Non-stoichiometric, carbon-containing crandallite from Guatemala and plumbogummite from Cumbria have been characterized using electron microprobe (EMPA) and wet-chemical analyses, Rietveld analysis of powder X-ray diffraction (PXRD) patterns, and infrared (IR), Raman and cathodoluminescence (CL) spectroscopies. The samples contain 11.0 and 4.8 wt.% CO2, respectively. The IR spectra for both samples show a doublet in the range 1410–1470 cm–1, corresponding to CO3 vibrations. Direct confirmation of CO3 replacing PO4 was obtained from difference Fourier maps in the Rietveld analysis. Carbonate accounts for 67% of the C in the plumbogummite and 20% of the C in the Guatemalan crandallite, the remainder being present as nano-scale organic carbon. The CO3 substitution for PO4 is manifested in a large contraction of the tetrahedral volume (14–19%) and by a contraction of the a axis, analogous to observations for carbonate-containing fluorapatites. Stoichiometric crandallite from Utah was characterized using the same methods, for comparison with the non-stoichiometric, carbon-bearing phases.

Charoite, ideally (K,Sr,Ba,Mn)15–16(Ca,Na)32[(Si70(O,OH)180)](OH,F)4·nH20, is a rock-forming mineral from the Murun massif in Yakutia, Sakha Republic, Siberia, Russia, where it occurs in a unique alkaline intrusion. Charoite occurs as four different polytypes, which are commonly intergrown in nanocrystallme fibres. We report the structure of charoite-96 (a = 32.11(6), b = 19.77(4), c = 7.23(1) Å, β = 95.85(9)°, V = 4565(24) Å3, space group P21/m), which was solved ab initio by direct methods on the basis of 2676 unique electron diffraction reflections collected by automated diffraction tomography and refined to R1/wR2 = 0.34/0.37. The structure of charoite-96 is related to that of the charoite-90, which was also solved recently. Both structures are composed of three different types of dreier silicate chains running along [001] and separated by ribbons of edge-sharing Ca- and Na-centred octahedra. In the structure of charoite-96, adjacent blocks formed by three different silicate chains and stacked along the x axis, are shifted by a translation of 1/2 c. The shifts involve a hybrid dreier quadruple chain, [Si17O43]18– and a double dreier chain, [Si6O17]10–. In charoite-90 adjacent blocks are stacked without shifts.

A quantitative determination of Fe3+/ΣFe ratios using the electron microprobe is presented for glasses. The measurements are based on the shift of the Fe-Lα peak position between Fe3+ and Fe2+, resulting from differences in self-absorption. We present new calibration curves for glasses with Fe contents as low as 2 wt.% Fe.

This method was used for glasses from a metasomatized spinel Iherzolite (Massif Central, France) in which highly vesicular glass associated with secondary minerals occurs in reaction pockets around corroded Cr-spinels. The glass was found to be oxidized homogeneously with Fe3+/ΣFe ≈ 0.70 (measured with an uncertainty of ±0.06), in contrast with the value of ∼0.15 that would correspond to the former melt under fo2 conditions inferred from secondary minerals. The glass oxidation probably results from the dissociation of the melt-water content under degassing, prior to local hematite depositions (spinel rims and crack fillings).

Transmission X-ray diffraction is demonstrated as a new tool for examining daughter minerals within sub-micrometre-size fluid inclusions in fibrous diamond. In transmission geometry, the X-ray beam passes through the sample, interacting with a volume of material. Fibrous diamonds from Mbuji-Mayi. Democratic Republic of Congo; the Wawa area, Ontario, Canada; and the Panda kimberlite, Ekati Mine, Northwest Territories and the Jericho kimberlite, Nunavut, Canada were analysed using X-rays from a high-brilliance lab source and a synchrotron source. Daughter minerals present include the mica-group mineral celadonite, sylvite, halite, dolomite and other carbonates. This represents the first positive identification of halide minerals in fibrous diamond. Mineral inclusions such as forsteritic olivine and pyrope garnet were also found. Unexpectedly, daughter minerals were identified in only ten of the 38 diamonds analysed, despite their concentrations being greater than experimentally proven detection limits. The presence of significant amounts of amorphous or dissolved material appears unlikely, but cannot be ruled out. Alternatively, the results may indicate a wide variety of related daughter minerals, such that most phases fall below the detection limits. Transmission X-ray diffraction should be applied cautiously to the study of fibrous diamond, as it provides an incomplete account of the fluid-inclusion mineralogy.

The pre-Caledonian NYF Skoddefjellet pegmatite in Wedel Jarlsberg Land, Svalbard, contains xenotime-(Y) that is partly replaced by fluorapatite-hingganite-(Y) reaction coronas. Hingganite-(Y) contains up to 2.0 wt.% of Gd2O3, 4.7 wt.% of Dy2O3, 3.3 wt.% of Er2O3 and 5.5 wt.% of Yb2O3. Such unusual, previously undescribed, xenotime-(Y) breakdown was caused by Ca- and F-bearing fluids interacting with the pegmatite. The occurrence of hinnganite-(Y) as a breakdown product of xenotime-(Y) implies that a Be-bearing phase (beryl in this case) was also involved in the reaction. There are few Ca-bearing primary phases in the pegmatite, indicating that the source of fluid was probably located in the generally Ca-richer host rocks (metasediments), though the fluid composition was modified during metasomatism of the pegmatite (i.e. beryl dissolution).

The unit-cell parameters of andalusite and sillimanite have been measured by high-T powder X-ray diffraction up to 1000°C at ambient pressure. Within the temperature range investigated, all the unit-cell parameters varied smoothly, indicating no phase transition. The volume-temperature data were fitted with a polynomial expression for the thermal expansion coefficient (αT = a0 + a1T + a2T-2). yielding a0 = 2.55(2) × 10–5K–1, al = 0 and a2 = 0 for andalusite, and a0 = 1.40(4) × 10–5K–1a1 = 7.1(8) × 10–9K–2 and a2 = 0 for sillimanite. Using the new thermal expansion data determined in the present study and compressional data from the literature, the P-T phase relations of the kyanite-andalusite-sillimanite system were calculated thermodynamically, with the invariant point located at ∼523°C and 3.93 kbar.

Bassoite, ideally SrV3O7·4H2O, is a new mineral from the Molinello manganese mine, Val Graveglia. eastern Liguria, northern Apennines, Italy. It occurs as black euhedral to subhedral grains up to 400 urn across, closely associated with rhodonite, quartz and braunite. Bassoite is opaque with a sub-metallic lustre and a black streak. It is brittle and neither fracture nor cleavage was observed; the Vickers micro-hardness (VHN100) is 150 kg/mm (range 142—165; corresponding to a Mohs hardness of 4—41/2). The calculated density is 2.940 g/cm3 (on the basis of the empirical formula and X-ray single-crystal data). Bassoite is weakly bireflectant and very weakly pleochroic from grey to a dark green. Internal reflections are absent. The mineral is anisotropic, without characteristic rotation tints. Reflectance percentages (Rmin and Rmax) for the four standard COM wavelengths are 18.5%, 19.0% (471.1 nm); 17.2%, 17.8% (548.3 nm); 16.8%, 17.5% (586.6 nm) and 16.2%, 16.8% (652.3 nm), respectively.

Bassoite is monoclinic, space group P21/m, with unit-cell parameters: a = 5.313(3) Å, b = 10.495(3) Å, c = 8.568(4) Å, β = 91.14(5)°, V= 477.7(4) Å3, a:b:c = 0.506:1:0.816, and Z = 2. The crystal structure was refined to R1 = 0.0209 for 1148 reflections with Fo > 4σ(Fo) and it consists of layers of VO5 pyramids (with vanadium in the tetravalent state) pointing up and down alternately with Sr between the layers (in nine-fold coordination). The nine most intense X-ray powder-diffraction lines [d in Å (I/I0) (hkt)] are: 8.5663 (100) (001); 6.6363 (14) (011); 3.4399 (14) (1̄21); 3.4049 (17) (121); 2.8339 (15) (1̄22); 2.7949 (11) (122); 2.6550 (15) (200); 2.6237 (11) (040) and 1.8666 (15) (240). Electron microprobe analyses produce a chemical formula (Sr0.97Ca0.02Na0.01)V3.00O74H20, on the basis of 2(Sr+Ca+Na) = 1, taking the results of the structure refinement into account. The presence of water molecules was confirmed by micro-Raman spectroscopy. The name honours Riccardo Basso (b. 1947), full professor of Mineralogy and Crystallography at the University of Genova. The new mineral and mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification, IMA (2011-028).

Available experimental data on chemical composition and crystal structure of K-bearing clinopyroxenes are compiled together with the results of atomistic simulations and thermodynamic calculations of mineral equilibria. It is shown that the limited solubility of K2O in clinopyroxene from crustal rocks cannot be ascribed to the strong non-ideality of mixing between diopside (CaMgSi2O6) and K-jadeite (KAlSi2O6) components. The more likely reason is the instability of the potassic endmember with respect to other K-bearing phases. As the volume effects of typical K-jadeite-forming reactions are negative, the incorporation of K in the clinopyroxene structure becomes less difficult at higher pressure. Atomistic simulations predict that the thermodynamic mixing properties of diopside-K-jadeite solid-solutions at high temperature approach those of a regular mixture with a relatively small positive excess enthalpy. The standard enthalpy of formation (ΔfH° = —2932.7 kJ/mol), the standard volume (V° = 6.479 J mol–1 bar–1) and the isothermal bulk modulus (K0 = 145 GPa) of K-jadeite were calculated from first principles, and the standard entropy (S° = 141.24 J mol–1 K–1) and thermal-expansion coefficient (α = 3.3 x 1CP–5 K–1) of the K-jadeite endmember were estimated using quasi-harmonic lattice-dynamic calculations based on a force-field model. The estimated thermodynamic data are used to compute compositions of K-bearing clinopyroxenes in diverse mineral assemblages within a wide P-T interval. The review substantiates the conclusion that clinopyroxene can serve as an effective container for K at upper-mantle conditions.

Cossaite, ideally (Mg0.5,☐)Al6(SO4)6(HSO4)F6·36H20, was found in the altered pyroclastic breccia of an active fumarole (T about 350°C) located at the rim of the La Fossa crater, Vulcano Island, Aeolian archipelago, Sicily, Italy. Cossaite is trigonal, space group R3̄, with a = 22.010(2), c = 9.238(1) Å, V = 3875.6(6) Å3, Z = 3. It forms stout prismatic hexagonal crystals up to 100 μm in size, terminated by rhombohedral faces, and is associated with thermessaite, vlodavetsite, sassolite and salammoniac. Cossaite is colourless to white, the streak is white and the lustre vitreous. It is not fluorescent in either long-wave or short-wave ultraviolet radiation. The calculated density is 2.075 g cm–3. The mean refractive index nobs is 1.49(1) (589 nm). Chemical analysis gave MgO 1.4, A12O3 19.5, SO3 34.7, F 5.7, (H2O 40.85, from structure refinement), O=F –2.4, total 99.75 wt.%, corresponding to the empirical formula Mg0.56Al6.19S7.01H73.37F4.85O65.15 calculated on the basis of 70 oxygen plus fluorine atoms. The strongest six lines in the X-ray powder diffraction pattern [dobs(Å) (I) (hkl)] are: 4.15 (100) (140), 3.87 (70) (32̄2), 11.00 (50) (110), 4.58 (25) (131), 2.770 (20) (3̄33), 2.166 (20) (1̄8̄1). The crystal structure was refined to a final R index of 0.0349. It contains octahedral [A1(H2O)5F]2+ cations and sulphate anions interacting via hydrogen bonds to form channels running along [001], where disordered [Mg(H2O)6]2+ cations and hydrogensulphate anions are hosted.

The new mineral anorpiment, As2S3, the triclinic dimorph of orpiment, has space group PI and cell parameters a = 5.7577(2), b = 8.7169(3), c = 10.2682(7) Å, α = 78.152(7), β = 75.817(7), γ = 89.861(6)°, V = 488.38(4) Å3 and Z = 4. It occurs at the Palomo mine, Castrovirreyna Province. Huancavelica Department, Peru. It is a low-temperature hydrothermal mineral associated with dufrenoysite, muscovite, orpiment, pyrite and realgar. It occurs in drusy crusts of wedge-shaped, transparent, greenish yellow crystals. The streak is yellow. The lustre is resinous on crystal faces, but pearly on cleavage surfaces. The Mohs hardness is about VA. The mineral is sectile with an irregular fracture and one perfect and easy cleavage on ﹛001﹜. The measured and calculated densities are 3.33 and 3.321 g cm–3, respectively. All indices of refraction are greater than 2. The mineral is optically biaxial (—) with 2V = 35—40° and no observed dispersion. The acute bisectrix (X) is approximately perpendicular to the ﹛001﹜ cleavage. Electron microprobe analyses yielded the averages and ranges in wt.%: As 58.21 (57.74–59.03), S 38.72 (38.33–39.00), total 96.94 (96.07–97.75), providing the empirical formula (based on 5 atoms) As1.96S3.04. The strongest powder X-ray diffraction lines are [d (hkl) I] 4.867(002) 97, 4.519 (110,11̄1) 77, 3.702 (1̄1̄1) 46, 3.609 (022,11̄2) 82, 2.880(201,02̄2,1̄2̄1,023) 75, 2.552 (1̄13,1̄31,132) 100, 2.469 (114,130,13̄1) 96. The structure of anorpiment [R1 = 0.021 for 1484 reflections with F0 > 4σ(F)] consists of layers of covalently bonded As and S atoms. Each S atom bonds to two As atoms at As—S—As angles between 100.45 and 104.15°. Each As atom is strongly bonded to three S atoms at S—As—S angles between 91.28 and 103.59°, forming an AsS3 pyramid with As at its apex. The As—S linkages within the layers form rings of six AsS3 pyramids. Interlayer bonding forces are interpreted as van der Waals. The structure of anorpiment is similar to that of orpiment in that it is composed of layers of As2S3 macromolecules, but arranged in a different stacking sequence.

Oscillatory zoning in solid solutions of alums ((K,NH4)Al(SO4)2·12H2O, K(Al,Cr)(SO4)2·12H2O, (K,Rb)Al(SO4)2·12H2O) and nitrates of divalent metals ((Sr,Pb)(NO3)2, (Ba,Pb)(NO3)2) grownfrom low-temperature aqueous solutions is considered. The zoning is detected by means of X-ray diffraction topography, crystal optics and electron probe microanalysis and involves variations of the crystal composition and degree of the growth ordering of atoms. The zoning patterns are very different in the predominant ﹛111﹜ and ﹛1̄11﹜ and subordinate ﹛100﹜ and ﹛110﹜ growth sectors. The different types of micromorphological instabilities of a growing face are suggested to explain the origin of the observed zoning.

Sveinbergeite, Ca(Fe2+6Fe3+)Ti2(Si4O12)2O2(OH)5(H2O)4, is a new astrophyllite-group mineral discovered in a syenite pegmatite at Buer on the Vesteroya peninsula, Sandefjord, Oslo Region, Norway. The mineral occurs in pegmatite cavities as 0.01—0.05 mm thick lamellar (0.2—0.5×5—10 mm) crystals forming rosette-like divergent groups and spherical aggregates, which are covered by brown coatings of iron (and possibly manganese) oxides, associated with magnesiokatophorite, aegirine, microcline, albite. calcite, fluorapatite, molybdenite, galena and a hochelagaite-like mineral. Crystals of sveinbergeite are deep green with a pale green streak and a vitreous and pearly lustre. Sveinbergeite has perfect cleavage on ﹛001﹜ and a Mohs hardness of 3. Its calculated density is 3.152 g/cm3. It is biaxial positive with α 1.745(2), β 1.746(2), γ 1.753(2), 2V(meas.) = 20(3)°. The mineral is pleochroic according to the scheme Z > X ∽ Y : Z is deep green, X and Y are brownish green. Orientation is as follows: X ┴ L (001), Y ᶺ b = 12°, Z = a, elongation positive. Sveinbergeite is triclinic, space group P1̄, a = 5.329(4), b = 11.803(8), c = 11.822(8) Å; α = 101.140(8)°, β = 98.224(8)°, γ = 102.442(8)°; V = 699.0(8) Å3; Z = 1. The nine strongest lines in the X-ray powder diffraction pattern [d in Å(I)(hkl)] are: 11.395(100)(001,010). 2.880(38)(004), 2.640(31)(2̄10,l̄41), 1.643(24)(07̄1,072), 2.492(20)(2l̄l), 1.616(15)(070), 1.573(14)(3̄2̄2), 2.270(13)(1̄3̄4) and 2.757(12)(1̄40,1̄3̄2). Chemical analysis by electron microprobe gave Nb2O5 0.55, TiO2 10.76, ZrO2 0.48, SiO2 34.41, A12O3 0.34, Fe2O3 5.57, FeO 29.39, MnO 1.27, CaO 3.87, MgO 0.52, K2O 0.49, Na2O 0.27, F 0.24, H2O 8.05, O=F -0.10, sum 96.11 wt.%, the amount of H2O was determined from structure refinement, and the valence state of Fe was calculated from structure refinement in accord with Mossbauer spectroscopy. The empirical formula, calculated on the basis of eight (Si + Al) p.f.u., is (Ca0.95Na0.12K0.14)Σ1.21(Fe2+5.65Fe3+0.93Mn0.25Mg0.18)Σ7.01(Ti1.86Nb0.06Zr0.05Fe3+)Σ2 (Si7091Al0.09)Σ8O34.61H12.34F0.17, Z = 1. The infrared spectrum of the mineral contains the following absorption frequencies: 3588, ∽3398 (broad), ∽3204 (broad), 1628, 1069, 1009, 942, 702, 655 and 560 cm–1. The crystal structure of the mineral was solved by direct methods and refined to an R1 index of 21.81%. The main structural unit in the sveinbergeite structure is an HOH layer which is topologically identical to that in the astrophyllite structure. Sveinbergeite differs from all other minerals of the astrophyllite group in the composition and topology of the interstitial A and B sites and linkage of adjacent HOH layers. The mineral is named in honour of Svein Arne Berge (b. 1949), a noted Norwegian amateur mineralogist and collector who was the first to observe and record this mineral from its type locality as a potential new species.

Cu-bearing elbaite from Paraíba (Brazil) is a highly-prized gem tourmaline. Specimens of similar quality from localities in Mozambique and Nigeria are being sold, and reliable provenance tools are required to distinguish specimens from the original locality from ‘Paraíba-type’ tourmaline from Africa. Here we present Li and B isotope analyses of Cu-bearing elbaite from all three localities and demonstrate the suitability of these isotope systems as a provenance tool. Isotopic profiles across chemically zoned grains revealed homogenous B and Li isotopic compositions, demonstrating a strong advantage of their application as a provenance tool as opposed to major, minor or trace element signatures.

Li and B isotopes of all investigated samples of Cu-bearing elbaites from the three localities are within the range of previously published granitic and pegmatitic tourmaline. Anomalous isotope compositions published previously for these samples are corrected by our results.

The Zn-bearing beaverite of Sato et al. (2008) has been named ‘beaverite-(Zn)’ in accordance with the alunite supergroup nomenclature of Bayliss et al. (2010), and data for the mineral have been approved by the IMA-CNMNC. Beaverite-(Zn) occurs as a dark-brown secondary mineral in the hydrothermal Cu-Zn-Pb ore deposit of the Mikawa mine, Niigata Prefecture, Japan. Electron microprobe analysis gave an empirical formula of Pb0.95(Fe1.88Al0.10)(Zn0.83Cu0.03)(SO4)2[(OH)5.36O0.38] on the basis of S = 2. The Rietyeld analysis (Sato et al, 2008) indicated it to be trigonal, R3̄m, a = 7.3028(2), c = 17.0517(4) Å, V = 787.56(4) Å3.

The crystal structures of two polytypes of innelite, ideally Ba4Ti2Na2M2+Ti(Si2O7)2[(SO4) (PO4)]O2[O(OH)] where M2+ = Mn, Fe2+, Mg, Ca: innelite-1T, a 5.4234(9), b 7.131(1), c 14.785(3) Å, α 98.442(4), β 94.579(3), γ 90.009(4)°, V 563.7(3) Å3, space group P1̄, Dcalc = 4.028 g/cm3, Z = 1; and innelite-2M, a 5.4206(8), b 7.125(1), c 29.314(4) Å, 0 94.698(3)°, V 1128.3(2) Å3, space group P2/c, Dcalc.= 4.024 g/cm3, Z = 2, from the Inagli massif, Yakutia, Russia, have been refined to R values of 8.99 and 7.60%, respectively. Electron-microprobe analysis gave the empirical formula for innelite as (Ba3.94Sr0.06)Σ4.00(Na2.16Mn0.382+Fe2+0.17Mg0.15Ca0.10☐0.04)Σ3(Ti2.97Nb0.02Al0.02)Σ3.01Si4.01 (S1.02P0.81☐0.17)Σ2H1.84O25.79F0.21 which is equivalent to (Ba3.94Sr0.06)Σ4.00(Ti1.97Nb0.02Al0.02)Σ2.01 [(OH0.99F0.21)Σ1.20O0.80], calculated on the basis of 26 (O + F) anions, with H2O calculated from structure refinement. The crystal structure of innelite is a combination of a TS (titanium silicate) block and an I (intermediate) block. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral) and exhibits linkage and stereochemistry typical for Ti-disilicate minerals of Group III (Ti = 3 a.p.f.u.): two H sheets connect to the O sheet such that two (Si2O7) groups link to the trans edges of a Ti octahedron of the O sheet. The I block contains T sites, statistically occupied by S and P, and Ba atoms. In the structures of innelite-1T and innelite-2M, TS blocks are related by an inversion centre and a cy glide plane, respectively. HRTEM images show a coherent intergrowth of the two polytypes, together with an as-yet unidentified ∼10 Å phase.

Several bodies of moderately foliated and porphyroblastic metabasites crop out on the SE side of the metamorphic cover of the Karkonosze granite within metapelites of the Sowia Dolina area (West Sudetes, Saxothuringian zone). Depending on the microstructural setting of the Ca-amphiboles in the rocks, different mineral-chemical trends have been determined for Si, XMg, AlVI, A[Na+K] which serve as semi-quantitative indicators of temperature and pressure changes. Porphyroblasts and prisms oblique to the main foliation in schistose metabasites show zoning from Mg-hornblende and actinolite to tschermakite, and then to Mg-hornblende (or actinolite). Matrix amphiboles and those in pressure shadows around some porphyroblasts have tschermakitic cores and actinolitic rims. Rarely, Ca-amphibole is accompanied in schists by late- to post-tectonic cummingtonite. Thermobarometric calculations involving empirically calibrated amphibole equilibria enable a reconstruction of P-T paths for individual rocks and the unravelling of the metamorphic evolution of the metabasites. Peak metamorphic temperatures of 615–640°C and pressures of 7.3–8.2 kbar were preceded by a variably preserved earlier stage (T = 370–550°C, P = 2.8–6.2 kbar). The final metamorphic episode took place at 450–550°C and 2.5–4.8 kbar and is recorded particularly in rocks close to the Karkonosze pluton. The metabasites shed new light on the history of metamorphism in the Sowia Dolina area. The first two stages of MP-MT metamorphism, coeval with Variscan deformation events (continental collision, burial and subsequent exhumation), took place under epidote-amphibolite then amphibolite facies conditions. The last stage partly concurred with the final stages of Variscan deformation and overlapped the onset of thermal activity associated with the Karkonosze granite. This metamorphic event is documented by metabasites (occasionally cummingtonite-bearing) outcropping close to the granite. Finally, a prehnitebearing assemblage reflects retrograde re-equilibration under greenschist/sub-greenschist facies conditions (T <300–350°C, P <2.5–3 kbar), which might also be partly due to hydrothermal activity around the pluton.

Dellaite crystals of close to end-member composition, Ca6(Si2O7)(SiO4)(OH)2, and with ∼1.5 wt.% Cl. yielding Ca6(Si2O7)(SiO4)(OH)1.75Cl0.25 have been found in skarns within the gabbroid rocks of the Birkhin complex (Eastern Siberia, Russia). The greatest Cl content analysed in a dellaite domain in this skarn is 5.2 wt.% Cl corresponding to 0.8 Cl p.f.u. Dellaite occurs in altered merwmite-larnite-bredigite-gehlenite skarns and also in calcio-olivine skarns with residual larnite. The crystal structures of Cl-free and Cl-bearing (∼1.5 wt.% Cl) dellaite have been refined, including hydrogen positions, from single-crystal X-ray data to R1 = 3.7 and 3.8%, respectively. In addition, both dellaite varieties were studied by Raman spectroscopy indicating stronger hydrogen bonds for the Cl-bearing sample, which agrees with the structural data. Cl is strongly selective and enriches at one (O6) of the two OH positions allowing for the formation of a stronger hydrogen bond O8—H8…C16 compared to O8—H8…O6. Raman spectra of the domain with ∼0.8 Cl p.f.u. confirm the general enhancement of a low-frequency band in the OH range suggesting the dominance of the O—H…Cl hydrogen bond systems.

Dellaite and killalaite, Ca3.2(H0.6Si2O7)(OH), have related modular structures, differentiated only by the Si2O7 units in killalaite and alternating Si2O7 and SiO4 units in dellaite. The similarity in cell dimensions and chemical composition suggests that trabzonite, Ca4Si3Oi0-2H2O, with Si3Oi0 trimers also belongs to the same family of structures.