Alternating eclogitic amphibolites, mica schists and orthogneisses in the Schobergruppe to the south of the Tauern Window suffered a post-Upper-Ordovician progressive deformation D1-D2 which produced parallel planar-linear structures in all the rocks. Zoned garnets, preferentially oriented zoned clinopyroxenes (Jd 35-42%) and albite (An 7-9%) give evidence of high-pressure metamorphism (550-650°C 14-16 kbar) of the metabasites. Ca-amphiboles crystallized during subsequent decompression. In a kyanite-staurolite-garnet mica schist 300 metres below the metabasites, garnetbearing assemblages grew synchronous with the development of foliations S1 and S2. Garnets are zoned with increasing XMg and decreasing-increasing-rcdecreasing Xca from cores to rims. Albitic plagioclase (An 1-3%) and micas are enclosed in garnet cores and rims, are in contact with garnet, and occur with garnet in microlithons. When these minerals are used for geothermobarometry, a prograde P-T evolution (460 to 680°C with coeval pressure variations which reach high-pressure conditions can be estimated. This suggests that garnet-plagioclase geobarometry with albitic plagioclase works in the relevant P-T field. Similar garnet zonation trends and a similarly shaped P-T path from mica schists of an adjacent region with late-Variscan cooling ages, points to an eady-Variscan age of the syn-D1-D2 high-pressure and subsequent amphibolite-facies metamorphism.

Lamproites with high MgO, high SiO2 affinity are abundant only in SE Spain where the Cancarix outcrop (in the province of Albacete) occurs. The rocks of Cancarix are peralkaline, saturated to oversaturated in silica, very high in K2O, Th and LREE. The mineralogy and petrography show some variations which depend on the conditions of emplacement and rate of cooling of the magma. The following phases may be present: olivine, phlogopite, K-amphibole, clinopyroxene, sanidine, orthopyroxene, apatite, and, in minor amounts, Cr-spinel, minerals of the pseudobrookite group, ilmenite, roedderite, dalyite, carbonate, analcime (probably pseudomorphous on leucite), a silica phase, rutile, pyrochlore (?), britholite (?) and glass. The lamproites of Cancarix contain Cr-Zrarmalcolite, which is typical of lunar basalts and which has been found also in kimberlites. The composition of early magmatic spinel and the occurrence of Cr-Zr-armalcolite indicate low oxygen fugacity for the primitive magma and related mantle source, in agreement with recent experimental data on lamproitic systems. The redox conditions changed during crystallisation, leading to increase of the Fe3+/Fe2+ ratio in the system. During the later stages of crystallisation, the residual melts/fluids were depleted in alumina and enriched in several components, e.g. Na, Zr, Fe, REE, C1, etc. stabilising Na-Fe-clinopyroxene, dalyte, arfvedsonitic rims around K-richterite and other alumina-free phases which, on a chemical basis, have been identified as britholite and pyrochlore. Rough comparison with experimental systems and the geochemistry of the rocks suggests that the magma was generated at shallow depth (≪20 kbar) in the lithospheric mantle, which, after early depletion, underwent strong enrichment in many 'incompatible' elements.

Thermoluminescence (TL) studies of insulators, including crystals of minerals such as calcite, quartz or zircon, have resulted in the development of a wider range of applications in the fields of radiation dosimetry and archaeological and geological dating. Most conventional TL measurements are made by recording light emission during heating by means of broad-band optical filters and blue-sensitive photomultiplier tubes. Much more information may be gained by monitoring the details of the emission spectrum during thermoluminescence. TL spectra of minerals exhibit changes as a result of crystal purity, radiation dose, dose rate and thermal history. This paper exemplifies the additional information available as a result of spectral studies, and focuses on investigations undertaken by the University of Sussex TL group. Examples include work on calcite, fluorite, zircon and feldspars.

The symmetry of diamond is still sometimes questioned. Most people agree that diamond belongs to the space group Fdm and therefore to point group . Some however, on account of the existence of a few natural tetrahedral diamonds, have assigned diamond to the point group 3m. We report here on an X-ray topographic investigation, using both conventional and synchrotron sources, of eleven natural tetrahedral diamonds. Two large specimens (from the Alpheus Williams' collection) were studied and found to consist of two portions, unequal in size, that were twinned on a (111) plane. Another diamond (from Professor R. A. Howie's collection) was found to contain two non-parallel (111) twin planes with the diamond filling the space between them, giving the crystal a tetrahedral morphology. Four tetrahedral diamonds (selected by Tolansky) were shown to be either twinned on a (111) plane, or cleavage fragments consisting of one component of a made or single crystals that had been plastically deformed. Similar results were found for some diamonds from the Argyle Mine. Our findings are consistent with diamond belonging to the holosymmetric class () rather than to the hemihedral class (3m).

Unusual irregular galena crystals and whiskers were found in close proximity in some druse cavities from the Gradishtc hydrothcrmal lead-zinc deposit in the Madan ore district, Bulgaria. The following crystal forms were observed: (1) straight thin [110] whiskers and thicker needles; (2) kinked whiskers; (3) curvilinear whiskers; (4) complex tortuous whiskers composed of segments with varying directions—[110], [100], [211], (5) thicker irregular elongated crystals. Combinations of these forms occur also. The detailed SEM study shows that all these formations are single crystals of extreme anisometricity, bounded by octahedral and cubic faces as well as by stepped surfaces of these forms. Surface structures such as longitudinal grooves, jagged edges, striations, pits, etc., are abundant.

It is assumed that these highly non-equilibrium crystals with large surface areas were formed through rapid directed growth from highly supersaturated solutions under a diffusional regime. Such special environments arose in the ore veins as a result of tectonic shocks leading locally to a drastic volume increase and P and T decrease in the solutions.

A Bi-Ni-Co vein in the contact zone of a granite near Pozoblanco, Córdoba, Spain, shows a zoned structure with mm-thin quartz wall zones, up to 20 cm thick Bi-rich quartz zones, and a few cm thick quartz-bismuth transition zones grading into a central quartz vug zone. The Bi-rich zones show textures indicating a metacolloidal origin from a silica gel enriched in adsorbed Bi: (1) globular and chain aggregates of fine-granular allotriomorphic quartz represent morphological relics of a globulated silica gel; (2) quartz rosettes, chain rosettes and stringer-combs radiating from the quartz globules and chains represent crystallised silica gel matrix; (3) crack fillings of quartz, gersdorffite and platy bismuth dendrites represent precipitates of metal-saturated dilute hydrosols filling shrinkage cracks in the desiccating and crystallising gel; (4) quartz spherocrystals in rosettes and combs are clouded with colloidal particles inherited from the silica gel; (5) unsupported wall rock inclusions represent inclusions in a viscous silica gel precursor covering fissure walls. The thin wall zones are quartz fillings of cracks between shrinking gel and walls. The transition and vug zones are recrystallised colloidal silica crusts precipitated by fissure-filling rest-solutions. Tree-like bismuth-gersdorffite dendrites in the transition zones are precipitates of metal-rich solutions infiltrating from the Bi-rich zones into the recrystallising silica crusts. The pre-concentration of metals in silica gels explains the dendrite formation without assuming abnormally high metal concentrations in transporting solutions or long range diffusion processes.

K-edge X-ray absorption spectra of Fe in garnet samples from the Ivrea-Verbano zone were collected using synchrotron radiation. From XANES analysis, the prevalent oxidation state of Fe has been determined as 2+ in all studied samples. Coordination numbers and Fe-O bond lengths derived from the EXAFS analysis are compatible with a dodecahedral environment of Fe atoms and seem to be nearly independent of the variable Fe/Ca ratio of the cations sharing the dodecahedral site in these garnets. This suggests that, since at least up to 0.5 Ca atoms p.f.u, no sensible deformation of the dodecahedron geometry is sensed by the Fe cations, iron might strongly compete with Ca atoms in controlling the entry of rare earth elements in the dodecahedral site of garnets falling within this compositional range. Comparison of the EXAFS results with the data from single crystal X-ray diffraction structure refinements indicates a first shell neighbour distance accuracy of ±0.02 Å, using theoretical EXAFS phases and amplitudes. The Debye-Waller factors derived from the EXAFS analysis indicate a higher degree of disorder on the four longer Fe-O bond distances, in comparsion with the other four shorter distances of the height-coordinated cation; this could be related to the nonrigid polyhedral behaviour of the dodecahedral site.

Compositional variations with respect to minor elements A1, Cr, Ti and Mn, and major elements Fe and Mg, in orthopyroxenes along ca. 160 km of strike of the Lower (LZ), Lower Critical (LCZ) and Upper Critical (UCZ) Zones are reviewed on the basis of 1900 analyses by electron microprobe. AI increases with stratigraphic height and declining Mg/(Mg + Fe2) ratios (hereafter MMF ratios) through the LZ and LCZ, reaching peak values close to the base of the UCZ, where the first cumulus plagioclase appears in the succession. Above this, Al contents decline as MMF ratios decline. Through the same interval, subdued increase in Ti occurs through >1000 m of ultramafic cumulates, but this increase accelerates within the ca. 450 m UCZ sequence. Mn increases linearly with declining MMF ratios through the entire succession, Cr levels are highest in orthopyroxenes of the ultramafic LZ and LCZ, and olivine norites of the UCZ, but decline in more evolved norites and associated anorthosites of the UCZ.

This pattern of cryptic variations, displayed by a thick succession of cumulates, is consistent with the model of Bence and Papike (1972) and Grove and Bence (1977) for basaltic rocks, which links the levels of minor elements in pyroxenes with entry of plagioclase into the paragenesis.

Zoned barian muscovite (2.52-5.66% BaO) and unzoned biotite (0.99-1.77% BaO) occur in two amphibolite grade metacherts of the Alpine schists, Southern Alps, New Zealand. The Ba-micas are associated with quartz-chlorite-Mn-garnet-tourmaline-apatite-sulphide ± oligoclase ± rutile ± magnetite ± ankerite. Increasing Ba (core to rim) in the muscovite is accompanied by a decrease in Si, Ti, Fe + Mg, and K and an increase in [4]Al, [6]Al, and Na. The main substitution that accounts for entry of Ba into both micas is [A]Ba2+ + [4]Al3+ ⇋ [A]K+ + [4]Si4+ and possibly [A]Ba2+ ⇋ [A]K+ + □. Compositional variation of the muscovite is also governed by the substitutions, [6]Al3+ + [4]Al3+ ⇋ [6](Mg,Fe)2+ + [4]si4+, and [A]Na+ ⇋ [A]K+. The presence or absence of oligoclase, rutile, magnetite and Mg/(Mg + Fe) ratio of coexisting biotite control the Na, Ti, Fe and Mg contents of muscovite in the respective metacherts. Important variables controlling the occurrence of Ba-mica is the Ba-rich composition of the metacherts (1387 and 2741 ppm Ba) and metamorphic grade. In metacherts, siliceous and quartzofeldspathic schists with <1000 ppm Ba barium increases with increasing K2O content indicating that in K-feldspar-absent rocks barium is mainly contained in micas (<0.70% BaO). In greenschist facies metacherts and siliceous schists with high Ba (>1000 ppm) and low K2O, barian micas are not present and most of the Ba occurs in baryte ± barian carbonate with implication of a significant original hydrothermal-hydrogenous input. Although low grade illite/sericite/smectites containing Ba are the most likely precursor of the barian micas in the metacherts, strong marginal Ba enrichment in the muscovite indicates a later Ba-metasomatism resulting from the breakdown of baryte under reducing conditions during amphibolite facies metamorphism.

Within amphibolite facies Peninsular gneisses in the south of the Dharwar craton, units of Sargur supracrustal rocks contain ultrabasic enclaves. One of these enclaves is an orthopyroxenite which comprises bronzite, spinel and minor phlogopite preserving coarse-grained, relic textures of probable igneous origin. After incorporation into the gneisses the enclave evolved through several distinct stages, elucidation of which allow an assessment of its metamorphic history.

Firstly, deformation during closed system, anhydrous recrystallisation caused the coarse-grained textures to be partially overprinted by similar mineral assemblages but with a granoblastic texture. Secondly, open system hydration caused retrogression of the bronzite to alumino-gedrite at the margins of the enclave. Subsequently, the penetration of these fluids along grain boundaries caused reactions between spinel and bronzite to produce reaction pockets carrying assemblages of peraluminous sapphirine associated with cordierite and talc. The differences in the mineral assemblages in each pocket coupled with slight variations in their chemistry, suggest that equilibrium did not develop over the outcrop. Because sapphirine + magnesite is present in some pockets, it is evident that CO2 was also a component of the fluid.

Phase relations from the MASH portion of the FMASH system, to which the chemistry of the reaction pockets approximates, suggest that the hydrous metamorphism causing the changes depended upon the assemblage enstatite + spinel + vapour which exists at PT conditions above the position of I16, ∼760°C at 3 kbar and below I21 at ∼765°C at 5.6 kbar (Seifert, 1974, 1975), where sapphirine is replaced by kornerupine. The suggested path of reaction occurred between I18 and I21. Subsequent reactions related to I20 cause the formation of cordierite. Talc formation has to be modelled in a different reaction grid.

The metamorphism recorded by these reactions is thus at a maximum of amphibolite facies and is interpreted to have formed during the uplift and cooling history of the gneiss complex when hydrous fluids were free to migrate. Given the complex high-grade metamorphic history of this part of the Dharwar craton this event is likely to be late Archaean or Palaeoproterozoic in age.

Na-poor, Fe-bearing high sanidine from a lamproite near Cancarix (Spain) has 2Vα‖(010) = 37-43° and C2/m, a = 8.598(15), b = 13.050(26), c = 7.209(17) Å, β = 116.00(18)° V = 727(2) Å3. Rims of sanidine crystals against vugs contain up to 60 mole % KFeSi3O8 and up to 10 at.% Si and 6 at.% K above the stoichiometric requirement; otherwise, they have up to 4 mole % □Si4O8 and 3 mole % K2O.Si4O8 in solid solution. Their MgO content may reach 0.46 wt.%. The skeletons of mm sized blocky crystals (Baveno habit) indicate formation under moderate undercooling at temperatures not much above 725°C Feldspar formation was facilitated by a high diffusion rate due to low viscosity in a highly perpotassic melt, supersaturated by pressure release and diopside fractionation, upon extrusion of a huge volume of lava in a crater. After titanian potassium-richterite largely filled the interstices in the sanidine fabric, crystals of dalyite (K2ZrSi6O15) and Fe-rich rims of sanidine and amphibole crystals were formed from an increasingly hydrous, silicic, ferric, and peralkaline residual melt. High rate nonequilibrium crystallisation caused the incorporation of excess SiO2 and K2O in the defect structure of the sanidine. Retrograde boiling initiated the escape of volatiles, causing the quenching, by which the disordered structural state and the nonstoichiometric composition of the sanidine were preserved.

Uranyl-silicates are widespread minerals in oxidised parts of various uranium deposits, and they frequently contain associations of the polymorphic forms of uranophane. In several recent works devoted to the study of uranium deposits as natural analogues of high-level nuclear waste repository (HLNWR), uranophane is frequently mentioned but without determination of the exact polymorphic species. The existence of two polymorphs presenting different stabilities has to be taken into account when considering the long-term behaviour of these minerals and the use of thermodynamic models for predicting the radionuclide migration in HLNWR. We present here new crystallographic data on betauranophane, and preliminary results of synthesis experiments of uranyl silicates. XRD patterns and calculated parameters of beta-uranophane from a Mexican U-deposit are presented. Synthesis experiments succeeded in crystallising uranophane (alpha form) at different pH, Si-, Ca- and Na activities, but beta-uranophane was never obtained. The controlling physico-chemical parameters responsible for the occurrence of these two polymorphic forms are still unknown.

Gatehouseite is a new manganese hydroxy phosphate from Iron Monarch, South Australia. The new mineral occurs as radiating clusters of pale yellow, and yellow to pale brownish orange bladed crystals up to 100 ~tm in length. The crystals are elongated along [010] and the principal forms are {102}, {110} and {001}. Gatehouseite also occurs as overgrowths on prismatic arsenoclasite crystals. Associated with gatehouseite are baryte, shigaite, manganoan ferroan calcite, hausmannite and hematite. Gatehouseite appears to have formed at low temperature by the interaction of phosphorus-rich fluids on hausmannite in carbonate-rich fractures in the hematite ore. Electron microprobe analysis yielded: MnO 64.42, FeO 0.19, CuO 0.03, ZnO 0.03, PbO 0.05, Al2O3 0.10, P2O5 22.18, V2O5 0.38, As2O5 3.58, H2O (6.44%). These data gave an empirical formula of Mn5.09Fe0.01Al0.01(P1.75As0.17-V0.02)∑1.94O8(OH)4.00, calculated on the basis of 12 oxygen atoms. The simplified formula is Mn5(PO4)2(OH)4. The mineral is transparent with a pale yellow streak, an adamantine lustre and an estimated Mohs hardness of 4. The crystals exhibit a distinct cleavage on {010} and have a splintery fracture. The strongest lines in the X-ray powder pattern are (dobs, Iobs, hkl) 4.48 (10) (004); 4.03 (10) (104); 2.900 (100) (11.5); 2.853 (70) (106); 2.801 (50) (021); 2.702 (80) (303); 2.022 (15) (322); 1.608(15) (330). These data were indexed on an orthorhombic cell, with a = 9.097(2), b = 5.693(2), c = 18.002(10) Å and a volume of 932.4(8) Å3; the space group is probably P212121. For Z = 4 and using the empirical formula, the calculated density is 3.74 g/cm3. Optical properties could not be determined in full; two refractive indices are 1.74(1) and 1.76(1) (white light); pleochroism is distinct from brown to near colourless. The crystals are length slow with parallel extinction. The name is for Dr. Bryan Michael Kenneth Cummings Gatehouse (1932-), crystal chemist of Monash University, Melbourne, Australia.

The crystal structure of antimonian asbecasite in an ejectum of hypabyssal origin occurring at Tre Croci near Vetralla, Vico volcanic complex, Roman potassic province, Latium, Italy, has been refined to R = 0.042, and is compared to the original crystal structure determination carried out on the Sb-free asbecasite of hydrothermal metamorphic origin from the type-locality, Cherbandung in Binna valley, Monte Leone nappe, Switzerland. New electron microprobe analyses of samples from both localities demonstrate crystal-chemical features that permit distinction between asbecasites from the two occurrences, so far the only known localities for this mineral.

The crystal structure of the rare lead hydroxychloride paralaurionite [PbCI(OH), monoclinic, space group C2/m, a = 10.865(4), b = 4.006(2), c = 7.233(3) Å, β = 117.24(4)°] has been refined to R = 0.062, Rw = 0.048. Its Order-Disorder (OD) character and its OD relationships with the orthorhombic polytpe of PbCI(OH), laurionite, are discussed. Laurionite and paralaurionite represent the two MDO structures within a family of OD structures built up by two different kinds of layers. The structures of paralaurionite and laurionite are compared thoroughly. The first coordination of the various atoms in the two polytypes is the same, however, remarkable differences exist in the connection between adjacent Pb-centred polyhedra.

X-ray diffraction refinement of the crystal structure of eosphorite has been carried out with reference to the orthorhombic space group Cmca. The structure is similar to that previously described by Hanson (1960), but the standard deviations are improved. Optical absorption and photoluminescence have also been studied for this mineral. Two sharp emission lines, denoted as R1 and R2, superimposed to a broad band (630-750 nm) have been related to the presence of Cr3+ ions. The excitation spectrum of these emissions confirms that the absorption (excitation) bands centred at 431 nm and 585 are related to with 4A2 → 4T1 and 4A2 → 4T2 spin allowed transitions of this ion.

Interpretation of grain size measurements in terms of the kinetics of grain growth depends on the ability to define the temperature variation of mineral growth rates. An outline is presented of the application to mineral growth rates of a corresponding states equation (CSE), which provides a relationship of growth rate to a reduced temperature function. Additionally, growth rates exhibit a 'compensation effect' between the pre-exponential constant and the activation energy in the standard Arrhenius equation, analogous to that shown by diffusion data. The general systematics of activation energy, equilibrium temperature and growth rate maxima are controlled by the relationships of the CSE, the standard Arrhenius equation and the compensation effect, and on this basis the temperature variation of growth rate between the equilibrium and the glass temperature may he estimated.