Porosity occlusion has been studied in a granodiorite rock from the Peruvian Coastal Batholith. The texture of the granodiorite is characteristic of Cordilleran I-type rocks, and the textural relations and modelled crystallization path within the quaternary An-Ab-Or-Qz system indicate alkali feldspar was the last major phase to start crystallizing. In thin section, alkali feldspar crystals occur both as large anhedral ‘plates’ containing numerous inclusions, and small interstitial cuneiform ‘pockets’. The alkali feldspar pockets are interpreted as late stage nucleation and growth of new crystals in pores that became isolated from the larger crystals during the latter stages of crystallization. Their geometry therefore mirrors that of the pores immediately after isolation.

From the modal abundance of the interstitial pockets, and taking into account contemporaneous growth of the other major phases, it is suggested that crystallization in isolated pores involved solidification of the final 3–4% of liquid. Alkali feldspar growth on the rims of the large anhedral plates prior to pore isolation is evidence for the localised (mm-cm scale) diffusion of chemical species within the interconnected melt phase. However, Rayleigh number calculations indicate that the separation of melt from crystals by compositional convection is unlikely to have occurred during interstitial crystallization.

The structure of a synthetic sample of analcime has been determined as a function of temperature between 30–300 K by high-resolution neutron powder diffraction. Although there are some reports of samples of analcime having non-cubic structures, the sample in our experiments remained cubic (space group la3d), and hence disordered, down to low temperatures. The absence of phase transitions involving ordering of the orientations of the water molecules, ordering of the sodium positions, or a displacive instability as in leucite and related materials, is discussed. We speculate that part of the reason for the absence of ordering of the water molecules or sodium cations is associated with the Al/Si disorder, which cannot order at low temperatures. We also discuss the likely distribution of the orientations of the water molecules at low temperatures, and propose that the water diads lie close to any of the crystal diads with the H-H Vectors lying close to the triads.

Leisingite, ideally Cu(Mg,Cu,Fe,Zn)2Te6+O6·6H2O, is hexagonal, P3 (143), with unit-cell parameters refined from powder data: a = 5.305(1), c = 9.693(6) Å, V = 236.2(2) Å3, c/a = 1.8271, Z = 1. The strongest six reflections of the X-ray powder-diffraction pattern [d in Å (I) (hkl)] are: 9.70 (100) (001), 4.834 (80) (002), 4.604 (60) (100), 2.655 (60) (110), 2.556 (70) (111) and 2.326 (70) (112). The mineral is found on the dumps of the Centennial Eureka mine, Juab County, Utah U.S.A. where it occurs as isolated, or rarely as clusters of, hexagonal-shaped very thin plates or foliated masses in small vugs of crumbly to drusy white to colourless quartz. Associated minerals are jensenite, cesbronite and hematite. Individual crystals are subhedral to euhedral and average less than 0.1 mm in size. Cleavage {001} perfect. Forms are: {001} major; {100}, {110} minute. The mineral is transparent to somewhat translucent, pale yellow to pale orange-yellow, with a pale yellow streak and an uneven fracture. Leisingite is vitreous with a somewhat satiny to frosted appearance, brittle to somewhat flexible and nonfluorescent; H(Mohs) 3–4; D(calc.) 3.41 for the idealized formula; uniaxial negative, ω = 1.803(3), ɛ = 1.581 (calc.). Averaged electron-microprobe analyses yielded CuO 24.71, FeO 6.86, MgO 6.19, ZnO 0.45, TeO3 36.94, H2O (calc.) [21.55], total [96.70] wt.%, leading to the empirical formula based on O = 12. The infrared absorption spectrum shows definite bands for structural H2O with an O-H stretching frequency centered at 3253 cm−1 and a H-O-H flexing frequency centered at 1670 cm−l. The mineral name honours Joseph F. Leising, Reno, Nevada, who helped collect the discovery specimens.

The thermal expansion tensor of crocoite has been determined from high-resolution neutron time-of-flight powder diffraction data. The temperature dependence of the lattice constants between 4.5 K and 290 K have been fitted to a quasi-harmonic Einstein model, and the temperature dependence of the thermal expansion tensor has been calculated for 60 K ≤ T ≤ 290 K. The magnitudes of the principal expansivities and their orientation exhibit saturation behaviour for temperatures above 300 K. The predicted saturated expansion coefficients are α11 = 33.1(1) × 10−6K−1, α22 = 15.72(3) × 10−6K−1, α33 = 3.36(1) × 10−6K−1, with α22 parallel to b and α11 lying at an angle of −37.86(5)° to c for the P21/n setting of the crystal structure. The direction of maximum expansion is approximately parallel to both and the least-squares line passing through the projection of the chromium atoms on (010). The direction of minimum expansion lies approximately parallel to [101]. No evidence was found for either a structural or magnetic phase transition between 4.5 K and 300 K.

Noélbensonite, a new mineral, is the barium manganese analogue of lawsonite. It is described from the Woods ornamental rhodonite mine, 30 km NNE of Tamworth, New South Wales, Australia, where it occurs as aggregates of blocky to sometimes lamellar crystals ranging from a few micrometres to (rarely) 100 µm in length. It replaces NaMn amphibole, namansilite, and pectolite, and also occurs as tiny monomineralic veinlets 0.05–0.25 mm thick. Rare euhedral crystals are dominated by {100} and {011}, with (011) ^ = 68°. The mineral is orthorhombic, space group apparently Cmcm; a = 6.325(1), b = 9.120(1), c = 13.618(1) Å, V = 785.6(1) Å3, with a : b : c = 0.694 : 1 : 1.493. Noélbensonite is brittle, fracture irregular, Mohs hardness about 4, cleavage and twinning not observed, colour dark brown, streak paler yellow-brown, lustre earthy on some veinlet surfaces to brilliantly vitreous, calculated density 3.87 g/cm3, refractive indices α = 1.82(1),β (calculated from 2V) = 1.835(10), γ = 1.85(1), biaxial negative 2Vα = 46°(3°), strong dispersion r > v, straight extinction to plane of flattening, {100}, α ∥ c, β ∥ b, γ ∥ a with pleochroism in very thin sections: α = orange yellow, β = orange, γ = brownish orange, absorption γ > β ⇐p; α. The average of 23 electron microprobe analyses (wt.%) is SiO2 26.02, Al2O3 0.17, TiO2 0.01, Fe2O3 0.19, Mn2O3 34.76, CaO 0.31, Na2O 0.14, BaO 29.08, SrO 1.51, H2Ocalc 7.87, total 100.06, leading to the simplified formula . Up to 15% Sr and 9% Ca substitute for Ba in the large-cation sites. The strongest lines in the X-ray powder diffraction pattern are [(Iobs) dobs/Å hkl] (100) 4.85 111; (50) 4.557 020; (59) 4.322 021; (77) 3.416 113,004; (80) 2.869 202; (47) 2.849 114; (82) 2.729 024; (45) 2.543 132; (48) 2.428 222; (38) 2.255 223,041. The name is for William Noél Benson (1885–1957), in honour of his classic researches in the New England Fold Belt and of his tenure of the Chair of Geology at the University of Otago.

The crystal structure of carminite, PbFe2(AsO4)2(OH)2 has been refined. The mineral is orthorhombic, Cccm with a = 16.591(2), b = 7.580(1), c = 12.285(1) Å, Z = 8; the structure has been refined to a conventional R = 3.3% using 913 observed reflections [I>2σ(I)]. The structure contains stepped chains of edge-sharing pairs of Fe(O,OH)6 octahedra; these chains are linked by AsO4 tetrahedra and Pb atoms in distorted square antiprismatic co-ordination. The hydrogen bonding network in the structure has been modelled using bond valence calculations.

At a number of locations along the Pacific margin of the Americas and west Antarctica, small volumes of alkalic basalts were erupted following successive ridge crest-trench collisions. The basalts were generated as a result of upwelling of asthenosphere through windows in the subducted plate. There is no evidence for local high temperature mantle plumes or significant lithospheric extension associated with these basalts. For the best sampled area, the Antarctic Peninsula, mean values for fractionation-corrected iron content (FeO*) vary from 6.9 to 10.6 wt.%, and for Na2O (Na8.0) from 3.25 to 4.6 wt.%, implying generation of small melt-fractions at variable mean pressures. The results of rare earth element inversion modelling yield a melt generation interval of 100 to 52 km, with a maximum melt fraction of c. 7% generated from a MORB-like source at Tp 1300°C. Trace element and isotope systematics are also consistent with the generation of the basalts from a MORB-like source.

Mean pressures of melt generation increase with increasing distance from the original trench, but trace element and Na8.0 data suggest that there is no systematic variation in extent of melting with distance from the trench. The data are consistent with a model whereby a MORB melting column, initially intersecting the peridotite solidus at between 15 and 30 kbar, is truncated by a lithospheric cap which thickens from c. 15–20 km (≈ 5–8 kbar) up to a maximum of c. 50 km (≈ 15 kbar), such that the mean pressures of melting increase with increasing distance from the palaeo-trench. The MORB-like major element geochemistry of basalt samples closest to the ancestral trench are consistent with initial intersection of the peridotite solidus at low pressures (c. 15 kbar). For areas of thickest lithosphere, mean pressures of melt generation are higher, but extents of melting are lower than for a MORB melting column with a similar initial pressure of intersection of the peridotite solidus. All these basalts therefore potentially represent analogues for the small melt-fraction precursors to the generation of MOR tholeiites.

Thermal constraints suggest that these low volume, small melt-fractions, were generated with CO2 on the solidus, because mean pressures of melt generation are greater than the pressure of intersection of the Tp 1300°C mantle adiabat and the dry peridotite solidus. Potentially, all MORB may be generated initially with CO2 on the solidus, and if this is correct, it does not require thermal anomalies to generate large extents of melting at high mean pressures.

The Dabie Mountains is a collisional orogen between the North China and Yantze Continental plates. It is composed, from south to north, of the foreland fold and thrust belt alternated with molasse basin, the subducted cover and basement of the Yangtze continental plate, the meta-ophiolitic melange belt, the forearc meta-flysch nappe (bounded by southward and northward thrust belts) in which there may be a buried volcanic arc and a relict back-arc basin (Fig. 1A) (Xu et al., 1992a, 1994).

Ferroan and non-ferroan calcites occur in fractures in the Lower Carboniferous of the Variscan foreland of southern Belgium. These fractures post-date the Variscan orogeny and the calcites have a telogenetic origin. The non-ferroan calcites formed by recrystallization of the ferroan calcites. Two types of monophase aqueous fluid inclusions are present in the ferroan calcite cement. Although both types of inclusions formed at a temperature not exceeding 50°C, one type contains a moderately saline fluid (3.6–16.3 eq. wt.% NaCl) and the other type fresh water (Tm ice = 0°C). The fluid inclusions in the non-ferroan calcite also contain fresh water.

Detailed petrography of the fluid inclusions indicate that the fresh water migrated through the crystals along opened cleavage planes and microfractures. Therefore, they have a secondary origin. The recrystallization of the ferroan calcites to non-ferroan calcites occurred in this fresh water. The saline fluid inclusions are not related to the above mentioned microstructures and although their origin remains unknown, they could represent the ambient fluid from which the ferroan calcites precipitated. The study of the relationship between the occurrence of fluid inclusions and the microstructures seems promising for the identification of fluid inclusions representing post mineral formation fluid and temperature conditions in calcite cements.

Danalite is the Fe2+ end-member of the minerals of the helvite group, which have the general formula M8(BeSiO4)6S2, with M = (Mn,Fe2+,Zn). These minerals are relatively uncommon, although limited amounts are known at many localities round the world (e.g. Ragu, 1994; Larsen, 1988; Kwak and Jackson, 1986, and references therein). Their typical host rocks are skams, but occurrences in mineralized veins pegmatites, and altered alkali granites have also been reported. Danalite is rarer than helvite (Mn endmember) and genthelvite (Zn end-member) and, unlike the other two end-members, has never been found nor synthesized as a pure mineral (Mel'nikov et al., 1968).

Lead and lead minerals have been used for medical purposes throughout human history. For example, galena was used as an eye salve in pre-Dynastic Egypt and by the ancient Indian civilisations of Mohendro-Daro and Harappa some 3200 to 2800 B.C. (Nriagu, 1983). The use of lead and other heavy metals and their compounds in Ayurveda, the Hindu system of medicine, can be traced back to the first century A.D. when Jain and Buddhist healers began to encourage the use of these substances instead of animal products (Mukherjee, 1992).

During the study of some decay processes in marble covering the façade of the Florence Cathedral (1870-1887), vaterite was found as the principal component of some bonding mortars of inlay decorations.

Vaterite is one of the three polymorphous phases of CaCO3 and crystallizes in the hexagonal system, dihexagonal bipyramidal class (Kamhi, 1963; Sato and Matsuda, 1969): it is unstable under normal environmental conditions (Deer et al., 1964).

Olivines from igneous rocks generally have low calcium contents. However, olivines crystallized from strongly silica-undersaturated magmas occasionally contain large amounts of kirschsteinite (Ki" CaFeSiO4) and monticellite (Mo: CaMgSiO4) components. The purpose of this note is to report the first natural occurrence of kirschsteinite crystals that have lamite (La: CazSiO4) in the mineralogical norm.

Microwave dielectric heating methods for the preparation of a number of arsenate, phosphate, vanadate, molybdate and carbonate minerals and their deuterated analogues are reported; rapid and efficient syntheses of these have been achieved. The application of this to the study of vibrational spectroscopy of minerals is discussed, with particular reference to scorodite.

The Mg—Fe orthoamphibole series □ (Mg, Fe)7Si8O22(OH)2 — Na(Mg, Fe)5- Al2Si5Al3O22(OH)2 has an open end in the sense that the Si5 end member has not been found in nature; tiny domains of near end–member composition in intricately zoned crystals (Schumacher, 1980; Robinson et al. 1982), appeared to be intergrowths of two different double-chain silicates (Schumacher, pers. comm., 1994).

Ocean Drilling Program (ODP) Leg 147 recently drilled at Site 895 in Hess Deep (eastern Equatorial Pacific), where a structurally dissected section of the East Pacific Rise (EPR) is preserved, and intersected the mantle-crust transition zone of a fast-spreading centre for the first time. The core from Hole 895D (latitude 2°16.635′N, longitude 101°26.777′W) revealed that harzburgite is predominant over dunite in the top section of the Hole, but the reverse relationship is found lower in the section where dunite is closely associated with gabbroic rocks (gabbro and troctolite). Texture, mineralogy and mineral chemistry suggest a two-stage evolution for harzburgite preserved at the transition zone. Harzburgite with a porphyroclastic texture was produced by partial melting of peridotite to, or beyond the clinopyroxene-out phase boundary before or during asthenospheric (>1000°C) flow, which suggests a higher degree of mantle melting than normally expected below mid-ocean ridges. Subsequently, basaltic melt(s) interacted with this refractory harzburgite (olivine + orthopyroxene + spinel), which resulted in dissolution of orthopyroxene, re-equilibration and formation of olivine and spinel, and formation of clinopyroxene ± plagioclase, this is manifested as a progressive conversion of harzburgite to gabbroic rock through an intermediate dunite. At low melt/peridotite ratios, harzburgite was refertilised as the plagioclase component of the melt completely reacted with the peridotite matrix to produce clinopyroxene-spinel intergrowths and Al enrichment in ferromagnesian minerals. At high ratios, orthopyroxene completely dissolved incongruently, plagioclase appeared, and spinel was partially to completely resorbed; this produced olivine-bearing and olivine-free gabbroic rocks. Residual minerals in peridotites adjacent to gabbroic zones were enriched in Fe and Ti and depleted in Al.

Morinite, NaCa2A12(PO4)2(OH)F4.2H2O, is a lowtemperature hydrothermal phosphate found in granite and granite-pegmatite environments. It was first described by Lacroix in 1891 from Montebras, France (see Palache et al., 1951) where it occurred as rose coloured prismatic crystals with amblygonite, wardite, wavellite, apatite and cassiterite. Morinite is also known from Germany, Finland (Roberts et al., 1990) and the USA (Fisher and Runner, 1958; Fisher, 1960).