The new oxalate mineral antipinite is found in a guano deposit located on the Pabellón de Pica Mountain, Iquique Province, Tarapacá Region, Chile. Associated minerals are halite, salammoniac, chanabayaite, joanneumite and clays. Antipinite occurs as blue, imperfect, short prismatic crystals up to 0.1 mm × 0.1 mm × 0.15 mm in size, as well as their clusters and random aggregates. The mineral is brittle. Mohs hardness is 2; Dmeas = 2.53(3), Dcalc = 2.549 g cm–3. The infrared spectrum shows the presence of oxalate anions and the absence of absorptions associated with H2O molecules, C–H bonds, CO32–, NO3– and OH– ions. Antipinite is optically biaxial (+), α = 1.432(3), β = 1.530(1), γ = 1.698(5), 2Vmeas = 75(10)°, 2Vcalc = 82°. The chemical composition (electron-microprobe data, C measured by gas chromatography of products of ignition at 1200°C, wt.%) is Na2O 15.95, K2O 5.65, CuO 27.34, C2O3 48.64, total 99.58. The empirical formula is K0.96Na3.04Cu2.03(C2.00O4)4 and the idealized formula is KNa3Cu2(C2O4)4. The crystal structure was solved and refined to R = 0.033 based upon 4085 unique reflections with I > 2σ(I). Antipinite is triclinic, space group P1, a = 7.1574(5), b = 10.7099(8), c = 11.1320(8) Å, α = 113.093(1), β = 101.294(1), γ = 90.335 (1)°, V = 766.51(3) Å3, Z = 2. The strongest reflections of the powder X-ray diffraction pattern [d, Å (I,%) (hkl)] are 5.22 (40) (111), 3.47 (100) (032), 3.39 (80) (210), 3.01 (30) (033, 220), 2.543 (40) (122, 034, 104), 2.481 (30) (213), 2.315 (30) (143, 310), 1.629 (30) (146, 414, 243, 160).

Three almandine-rich metamorphic garnets have been studied by analytical electron microscopy and electron microprobe analysis. Electron microprobe analyses with total Fe calculated as Fe2+ show that there are no significant departures from stoichiometry due to the presence of Fe3+ in any of the garnets studied. However, in the transmission electron microscope (TEM) all the garnets were found to contain myriad spherical, iron-rich particles up to 400 Å in diameter. Microdiffraction techniques have revealed that the particles are a cubic spinel phase, consistent with magnetite. There is no crystallographic relationship between the host garnet and the particles, a rare situation for exsolution processes. The presence of such particles is interpreted in terms of the exsolution of magnetite from almandine garnet during cooling. This can apparently occur at temperatures below 55°C. The size of the particles is a qualitative indicator of the cooling rate of the rock, but is also dependent on the original Fe3+ content of the host garnet.

Seven manganese minerals have been observed in geodes from Chihuahua, Mexico. Ramsdellite occurs in a number of different habits, but the morphology and precession X-ray patterns suggest that it is pseudomorphous after groutite. Pyrolusite is found only in association with rams-dellite and is believed to be an alteration product of that mineral. Todorokite generally occurs as a late-stage fibrous overgrowth in many of the geodes. Ranciéite, birnessite, hollandite, and cryptomelane are present in trace amounts. This assemblage of manganese minerals is typical of supergene mineralization.

X-ray powder photographs reveal thomsonite a.s the principal product of some low-temperature hydrothermal experiments. Glasses of three compositions were used as starting materials; one of tile composition of anorthite (CaAl2Si2O8), one of a gallium-containing anorthite (Ca4[Ga3Al5]Si8O32) in which 3/8 of the Al is replaced by Ga, and a glass of the oxide composition of zoisite minus the water (4CaO. 3Al2O3. 6SiO2).

Unpublished work carried out in this laboratory several years ago had shown that the first-order basal X-ray reflections of illite from South Wales occurred at a spacing of about 10Å both with potassium- and calcium-saturated samples. Recently Jackson and others observed that hydrated mica samples having a 10Å basal spacing when saturated with potassium, showed a 12 to 13Å. spacing after saturation with calcium. They interpreted their results by ascribing to illite a limited capacity for reversible lattice shrinkage and expansion, identical in type with that known for montmorillonite.

In order to study the problem further three illite and two glauconite samples were treated with concentrated calcium chloride solutions for five weeks under frequent renewal of the solution.

The rocks of the lower and middle evaporite beds of the Permian, passed through by the D'Arcy Exploration Company's boring in 1938-39 (Lees and Taitt, 1946), have been described in earlier communications (Stewart, 1949, 1951). The present paper deals with the petrography of the upper evaporite bed (3655-3860 feet below surface).

A new kind of chromitite texture—a porphyritic nodular texture, found in an alpine-type complex in Pakistan, is described. The chromite from phenocrystic nodules and that from their disseminated chromitite groundmass show comparable trivalent elements and postcumulus to subsolidus Mg−Fe2+ variations, which are also recorded from ‘normal’ nodular ore samples. The nodular ores differ from all other textural types of chromitite from this complex in an unusual, though slight, increase in Cr/(Cr+Al) with Mg/(Mg+Fe2+) between stratigraphically different desposits, which is caused by magmatic differences. The implications of major element variations in chromites and olivines of nodular chromirites are discussed and a cumulus origin is supported. Temperatures of final chromite-olivine equilibration ranged from 750 to 900 °C the individual nominal values being higher for chromitite with coarser chromite crystals and, or, higher chromite:silicate ratio.

An investigation of the system Cu-Fe-O has established the existence of a phase near 3Cu2O.Fe3O4 and the non-existence of Cu2O.Fe2O3 a in the system over the range of oxygen pressures investigated.

The X-ray diffraction patterns obtained from four samples of natural delafossite have been found to be similar to that obtained from a synthetic sample of the 3Cu2O.Fe3O4 phase. It has also been shown that, when heated under equilibrium conditions in the thermobalance in air, a sample of natural delafossite and the synthetic 3Cu2O.Fe3O4 behaved similarly.

Over the past several decades, thinking about chemical processes in rocks had been dominated by experimental and theoretical treatments of mineral equilibrium, which is the state from which the time variable has been excluded. But, to an extent exceeding that of any of our sister sciences, we in geology are concerned with the behaviour of things as a function of time; thus equilibrium is but one of several interesting boundary conditions. Textures, (defined as the spatial relations within and among minerals and fluids, regardless of scale or origin) provide a means to sort out and identify successive states. In fact, it is the pattern of evolution of those states that enables us to deduce the processes. We may well draw the analogy with thermodynamics and kinetics, respectively:

equilibrium textures and phase assemblages, via thermodynamic analysis → definition of conditions of equilibration,

whereas

kinetics, as displayed in disequilibrium textures → sequence of events and processes of mineralization.

The interpretation of textures is one of the most difficult yet important aspects of the study of rocks and ores, and there are few areas of scientific endeavour that are more subject to misinterpretation. Although the difficulties are many, the opportunites for new understanding are also abundant. Textural interpretations have many facets: some are well established and accepted; some that are accepted may be wrong; others are recognised to be speculative and controversial; and we trust that still other textural features remain to be described and interpreted. This paper will deal principally with low-temperature, epigenetic ore deposits, and will emphasise silica and sphalerite; but extension to other materials is not unreasonable.

Ore and gangue minerals react internally, or with their environment, at widely ranging rates, ranging from the almost inert pyrite, arsenopyrite, well-crystallised quartz, and tourmaline to the notoriously fickle copper/iron and copper/silver sulfides. Arrested or incomplete reactions may be identifed by textural criteria and, when appropriately quantified, can provide guides to the duration of geological processes.

In recent years so much emphasis has been placed on isotopes, fluids, chemistry, and deposit and process models that the textural features have been ignored. In part this oversight occurs because we have grown accustomed to using superposition, cross-cutting, pseudomorphism, mutual intergrowths, exsolution and so on as off-the-shelf tools, to be grasped and applied without evaluation or even description. Surely science must build on previous work without constant and exhaustive reassessment, but for mineral textures a little reassessment may yield substantial benefit.

Mavlyanovite, ideally Mn5Si3, is a new mineral from a lamproite diatreme close to the upper reaches of the Koshmansay river, Chatkal ridge, Uzbekistan. It occurs together with unnamed manganese siliciphosphide and manganese silicicarbide minerals in round to ovoid segregations, up to 10 cm in diameter, in volcanic glass. Segregations of hexagonal prismatic mavlyanovite up to 1–2 mm occur in interstices in the matrix and tiny inclusions (1–2 μm) of alabandite and khamrabaevite occur within mavlyanovite. It is opaque with a metallic lustre, has a dark-grey streak, is brittle with a conchoidal fracture and a near-perfect basal cleavage. VHN100 is 1029–1098 kg/mm2 (Mohs hardness ~7). In plane-polarized reflected light, mavlyanovite is a pale-brownish-grey against the accompanying unnamed manganese silicicarbide (white). Reflectance values and colour data are tabulated. Average results of 19 electronmicroprobe analyses give Mn70.84, Fe 6.12, Si 22.57, Ti 0.15, P 0.18, total 99.86 wt.% leading to an empirical formula of (Mn4.66Fe0.40)5.06(Si2.91Ti0.01P0.02)2.94 based on8 a.p.f.u. The calculated density is 6.06 g/cm3, (on the basis of the empirical formula and unit-cell parameters from the structure determination). Mavlyanovite is hexagonal (P63/mcm) with a 6.8971(7), c 4.8075(4) Å, V 198.05(3) Å3 and Z = 2. The structure has been determined and refined to R1 = 0.017, wR2 = 0.044, GoF = 1.16. Mavlyanovite is the naturally-occurring analogue of synthetic Mn5Si3 which is the parent aristotype structure of the Nowotny intermetallic phases studied extensively by the material-science community. It is also the Mn-dominant analogue of xifengite Fe5Si3. The mineral name honours Academician Gani Arifkhanovich Mavlyanov (1910–1988), for his contributions to the understanding of the geology of Uzbekistan.

Back-scattered electron imaging with a scanning electron microscope was applied to the intimate association of fine chalcopyrite grains and sphalerite (‘chalcopyrite disease’) in synthesized products and natural specimens, in order to distinguish between diagnostic features of two formation mechanisms: replacement and coprecipitation. In the synthetic chalcopyrite disease in Fe-bearing sphalerite formed by a replacement reaction, chalcopyrite occurs as fine lamellae, which are also observed in relatively Fe-rich growth bands of the natural zoned sphalerite. Ellipsoidal to lens-like habits of chalcopyrite appear in sphalerite that has undergone extensive replacement reactions. These textures may have grown steadily from the lamellar chalcopyrite by consuming the FeS component dissolved in the sphalerite. All the sphalerite samples formed by the coprecipitation mechanism are Fe-poor, hosting triangular or irregularly bleb-like inclusions of chalcopyrite. This variety of chalcopyrite morphology could be attributed to diffusion rates and variations in fluid saturation, and their effect on the rate of crystal growth. Thus, in both replacement and coprecipitation the chalcopyrite habit depends strongly both on the FeS content of the host sphalerite and on kinetic factors, and is significant when interpreting chalcopyrite disease textures in natural samples.

Palladseite (palladium selenide) and palladian gold occur as euhedral inclusions in specularite and as infill of microfractures and interstices in magnetite aggregates (host rock fragments) within specularite-rich auriferous veins (jacutinga). Palladseite has minor amounts of Pt (0.6–3.5 wt.%), Cu (2.9–3.5 wt.%), Hg (0.9–1.9 wt.%), and Ag (0.3–0.5 wt.%). The palladian gold contains up to 6 wt.% Pd, and minor Cu and Ag. Isomertieite (Pd11Sb2As2) and sudovikovite (PtSe2) are also recorded. The veins cross-cut the main tectonic foliation of the wallrock (itabirite). The feature of fracture infill and the Se-Sb-As-Hg-Cu-Ag geochemical/mineralogical signature of the Au-Pd mineralization point to a post-ductile deformation and possibly low-temperature (epithermal) origin of the jacutinga mineralization style.

Palladseite is replaced locally by a Pd-rich oxidation phase. Electron microprobe analysis of alteration halos around palladseite yields 76–80 wt.% Pd. Oxygen calculated by stoichiometry accords with a monoxide compound of the type PdO. However, the measured oxygen content is lower than expected for the PdO stoichiometry, suggesting loss of volatile species, and a more ‘hydrated’ compound, such as an oxyhydroxide.

Marbles and interlayered coesite-bearing eclogites near the village ofSanqingge in the Sulu ultrahighpressure (UHP) terrane ofeastern China were studied to estimate their P-T evolution. Using garnet, omphacite and phengite as geothermobarometers, the coesite eclogites are calculated to have experienced P-T conditions of3.4 –3.7 GPa and ~600ºC (stage I), followed by decompression and a slight temperature decrease to 2.7–3.2 GPa and 520–560ºC respectively (stage II) and later to 2.6–2.8 GPa and ~500ºC (stage III). No water influx affected the eclogites until reaching amphibolite facies conditions of 0.5–1.3 Gpa and 595–685ºC (stage IV). As we interpret the occasional appearance ofcalcite with magnesite relics in the core as a reaction ofUHP dolomite and magnesite with Ca-rich fluids at stage IV to form CaCO3, the calculated pressure for stage I could be the maximum pressure experienced by these rocks. Thus, the crustal material ofthe Sanqingge quarry, originally sedimentary carbonates (now marbles) and interstratified basic tuffs (now eclogites), has been buried to a depth of ≥ 120 km at ~600ºC. This burial occurred in a subduction setting along a very low geotherm of 5–6ºC/km. The exhumation possibly occurred in the environment ofa subduction channel.

Kornerupine-rich layers up to several centimetres thick with minor sillimanite, spinel, Fe oxide and ilmenite occur in a diopsidite in sillimanite-cordierite gneiss south of Beraketa (24°27′S, 46°48′E), southern Madagascar. Kornerupine, sillimanite, spinel and hematite grains up to 1 mm across have mutual polygonal boundaries indicating textural equilibrium at their crystallisation. Kornerupine has XMg 0.67–0.80 and 0.9 to 2.6 wt.% B2O3. Sillimanite contains up to 2.0 wt.% Fe2O3. Spinel is essentially (Mg,Fe2+) Al2O4 with an XMg range of 0.29–0.40 and exsolution lamellae of Fe oxide. Textural relations demonstrate two limited reactions, each confined to areas less than 500 µm across: (1) Kornerupine and spinel reacted along grain contacts to form very fine-grained tourmaline, corundum and chlorite. The replacing phases are symmetrically zoned with a central tourmaline and hematite, bordered by an aggregate of chlorite, tourmaline and corundum, followed outwards by a rim of chlorite against the kornerupine and spinel. (2) Within kornerupine grains, zoned, round aggregates consist of very fine-grained chlorite, tourmaline and corundum of different composition than in (1). They define the terminal reaction of kornerupine breakdown.

Geothermobarometry indicates that the early kornerupine-bearing assemblage was stable at 7.0 kbar and 700 °C. This P-T point lies close to the retrograde, nearly isothermal trajectory defined independently by nearby sapphirine-bearing assemblages. The fine-grained aggregates formed most likely during further cooling, or by increasing water fugacity.

Leydetite, monoclinic Fe(UO2)(SO4)2(H2O)11(IMA 2012–065), is a new supergene uranyl sulfate from Mas d'Alary, Lodève, Hérault, France. It forms yellow to greenish, tabular, transparent to translucent crystals up to 2 mm in size. Crystals have a vitreous lustre. Leydetite has a perfect cleavage on (001). The streak is yellowish white. Mohs hardness is ∼2. The mineral does not fluoresce under long- or short-wavelength UV radiation. Leydetite is colourless in transmitted light, non-pleochroic, biaxial, with α = 1.513(2), γ = 1.522(2) (further optical properties could not be measured). The measured chemical composition of leydetite, FeO 9.28, MgO 0.37, Al2O30.26, CuO 0.14, UO340.19, SO321.91, SiO20.18, H2O 27.67, total 100 wt.%, leads to the empirical formula (based on 21 O a.p.f.u.), (Fe0.93Mg0.07Al0.04Cu0.01)Σ1.05(U1.01O2)(S1.96Si0.02)Σ1.98O8(H2O)11. Leydetite is monoclinic, space group C2/c, with a = 11.3203(3), b = 7.7293(2), c = 21.8145(8) Å, β = 102.402(3)°, V = 1864.18(10) Å3, Z = 4, and Dcalc = 2.55 g cm–3. The six strongest reflections in the X-ray powder diffraction pattern are [dobs in Å (I) (hkl)]: 10.625 (100) (002), 6.277 (1) (11), 5.321 (66) (004), 3.549 (5) (006), 2.663 (4) (008), 2.131 (2) (0 0 10). The crystal structure has been refined from single-crystal X-ray diffraction data to R1 = 0.0224 for 5211 observed reflections with [I > 3σ(I)]. Leydetite possesses a sheet structure based upon the protasite anion topology. The sheet consists of UO7 bipyramids, which share four of their equatorial vertices with SO4 tetrahedra. Each SO4 tetrahedron, in turn, shares two of its vertices with UO7 bipyramids. The remaining unshared equatorial vertex of the bipyramid is occupied by H2O, which extends hydrogen bonds within the sheet to one of a free vertex of the SO4 tetrahedron. Sheets are stacked perpendicular to the c direction. In the interlayer, Fe2+ ions and H2O groups link to the sheets on either side via a network of hydrogen bonds. Leydetite is isostructural with the synthetic compound Mg(UO2)(SO4)2(H2O)11. The name of the new mineral honours Jean Claude Leydet (born 1961), an amateur mineralogist from Brest (France), who discovered the new mineral.

Thermal aspects of the conflicting hypotheses that the acid magmas of the British Tertiary Igneous Province were generated by either fractional crystallization of basic magmas or partial fusion of country rocks around basic intrusions are investigated by combining petrological and experimental data. Sparse large xenoliths (up to 12 m2 outcrops) of Lewisian gneiss occur in the ferrodiorite member of the Marscoite Suite in the Western Redhills Eocene intrusive complex of Skye. Most of the blocks are of granodioritic-tonalitic gneiss which is very similar to the grey gneisses of the northern and southern regions of the mainland Lewisian. One is a two-pyroxene basic granulite, closely resembling in petrography and composition the granulite-facies basic gneisses of the central region of the Scottish mainland Lewisian. During Tertiary thermal metamorphism the xenoliths recrystallized patchily to pyroxene hornfelses and up to 50% of melting occurred in any parts of blocks that were rich in alkali feldspar and quartz. Microprobe analyses of intergrown Ca-rich and Ca-poor pyroxenes in a hornfelsed ultramafic mica pyroxenite lens within a leucogneiss block give a calculated temperature of 950 °C for the Tertiary metamorphism. Melting experiments at 1 kb PH2O were carried out on leucocratic and mesocratic Lewisian gneisses (from the xenoliths), Torridonian arkose and shale. Extensive melting of the leucogneiss and arkose, to peraluminous liquids, occurs within a few degrees above their solidus (715 °C). The silicate liquidus of the leucogneiss is at 930 °C. Microprobe analyses of the glass products of melting experiments (mostly of leucogneiss) show that liquid composition trends during progressive melting are consistent with theoretical equilibria in the synthetic system Ab-Or-An-Qz-H2O. Partial fusion in the Skye Lewisian gneiss xenoliths took place at a water vapour pressure of a few hundred bars, probably under water-undersaturated conditions.

The recent discovery of hyalophane [(K,Ba)Al1−2Si3−2O8] on the North range segment of the Early Proterozoic Cuyuna Iron Range of east-central Minnesota has shed new light on the depositional environment of these rocks. This Ba-feldspar occurs in a 10 m thick interval within the main iron-formation and typically contains between 8 and 26 mol.% celsian (BaAl2Si2O8). Its occurrence in several textural settings suggests that barium was being deposited at various stages in the paragenetic history of the iron-formation. Some of the hyalophane grains occur as the cores of micronodules, which are structurally similar to oolites or oncolites, but mineralogically are very complex. The hyalophane also occurs as rims on core grains of diverse mineral composition and as discrete phases in late crosscutting veins.

Hyalophane, like other Ba-silicates, has a very restricted paragenesis. They are associated typically either with sedimentary manganese and ferromanganese deposits, or with Cu-Pb-Zn-Ba deposits. The presence of hyalophane in the Early Proterozoic manganiferous iron ores of east-central Minnesota casts doubt on the historic interpretation of these deposits as typical Superior-type sedimentary iron-formations and instead supports the view that these deposits, at least in part, consist of chemical sediments from a hydrothermal fumarolic system. The suggested involvement of a hydrothermal system is also supported by the occurrence of aegirine within the hyalophane-rich layer, and the occurrence of tourmalinites and Sr-rich baryte veins elsewhere in the Cuyuna North range.