Garnet porphyroblasts, containing elongate ilmenite inclusions arranged in an essentially spherical pattern, are described. The garnets are post-tectonic, and the inclusion pattern is the result of deformation and simultaneous replacement of the matrix by the growing porphyroblast.

A new mineral majzlanite, ideally K2Na(ZnNa)Ca(SO4)4, was found in high-temperature exhalative mineral assemblages in the Yadovitaya fumarole, Second scoria cone of the Great Tolbachik Fissure Eruption (1975–1976), Tolbachik volcano, Kamchatka Peninsula, Russia. Majzlanite is associated closely with langbeinite and K-bearing thénardite. Majzlanite is grey with a bluish tint, has a white streak and vitreous lustre. The mineral is soluble in warm water. Majzlanite is monoclinic, C2/c, a = 16.007(2), b = 9.5239(11), c = 9.1182(10) Å, β = 94.828(7)°, V = 1385.2(3) Å3 and Z = 16. The eight strongest lines of the X-ray powder diffraction pattern are [d, Å (I, %)(hkl)]: 3.3721(40)($\bar{3}$12), 3.1473(56)($\bar{4}$02), 3.1062(65)($\bar{2}$22), 2.9495(50)($\bar{1}$31), 2.8736(100)($\bar{1}$13), 2.8350(70)(421), 2.8031(45)(511) and 2.6162(41)($\bar{5}$12). The following structural formula was obtained: K2Na(Zn0.88Na0.60Cu0.36Mg0.16)(Ca0.76Na0.24)(S0.98Al0.015Si0.005O4)4. The chemical composition determined by electron-microprobe analysis is (wt.%): Na2O 9.73, K2O 15.27, ZnO 11.20, CaO 7.03, CuO 4.26, MgO 1.07, Al2O3 0.47, SO3 51.34, SiO2 0.12, total 100.49. The empirical formula calculated on the basis of 16 O apfu is K1.99Na1.93Zn0.84Ca0.77Cu0.33Mg0.16(S3.94Al0.06Si0.01)O16 and the simplified formula is K2Na(Zn,Na,Cu,Mg)Σ2(Ca,Na)(SO4)4. No natural or synthetic compounds directly chemically and/or structurally related to majzlanite are known to date. The topology of the heteropolyhedral framework in majzlanite is complex. An interesting feature of the structure of majzlanite is an edge-sharing of ZnO6 octahedra with SO4 tetrahedra.

Psilomelane has been redefined from single crystal study to be of orthorhombic symmetry with the space group P222, the dimensions a 9·45, b 13·90, c 5·72 Å, and two molecules of per unit cell, where A represents Ba2+, Mn2+, Al3+, Fe3+, Si4+ etc., and X6 stands for (O,OH)6 with OH about 5. This formula is very closely followed by 14 analyses of psilomelane, and the calculated density agrees fairly well with the observed density. The powder data of psilomelane cannot be indexed with Wadsley's monoclinic cell and the conditions for the space group A2/m, proposed by Wadsley for his crystal, are not satisfied by the indexing. Wadsley's crystal was not psilomelane but probably an altered phase of Vaux's neotype specimen.

The electron micrograph of shining platy crystals of psilomelane shows some almost square-faced crystals whereas that of the botryoidal material consists only of particles with irregular edges. The dehydration product of psilomelane shows gradual shrinkage of the orthorhombic cell up to 500° C, marked structural changes at 600° C, and transformation at 800° C to a monoclinic phase, similar to hollandite.

Vlasovite, Na2ZrSi4O11, previously reported as monoclinic by Pyatenko and Voronkov from an occurrence in the Kola Peninsula, Russia, has been found in rocks from Ascension Island in a triclinic twinned modification. The obliquity is very slight (α and γ, differ from 90° by less than 1°), and X-ray photographs show arrays of paired spots corresponding to diffraction by different parts of the crystal related by the twinning operation, reflexion across (010).

On heating, this vlasovite is found to transform to the monoclinic variety at 29° C. The phase change has been followed on a single-crystal X-ray heating camera, and the obliquity is found to have successively smaller values as the crystal is heated from temperatures below room temperature to 29° C. The obliquity is characteristic of the particular temperature over the transformation range and is not affected by thermal history.

The transformation appears to be a displacive one, similar in some respects to α → β tridymite and α → β cristobalite, and some information has been obtained by X-ray structural investigations about the nature of the atomic movements involved.

As long ago as 1906 I had noticed a yellowish clay-like mineral occurring somewhat abundantly at both Cligga mine, Perranzabuloe, and at Bunny mine, St. Austell. From its appearance the mineral did not look particularly interesting, neither did it suggest being one containing a metal, and for these reasons no attempt was made to determine its character. In a paper read before this Society in 1937 I mentioned this yellowish clay-like substance as occurring associated with rashleighite at the Bunny mine. Soon after the publication of this paper in 1948 I received a letter from Monsieur N. Varlamoff in the Belgian Congo saying he had seen my reference to the 'yellowish clay-like substance' (p. 356) and suggested it might possibly be identical with the mineral varlamoffite which he had recently discovered in the Belgian Congo and which had been named after him, his description of the mineral with analysis, mode of occurrence, and localities having been published in 1948.

The pearceite-polybasite group of minerals, general formula [M6T2S7][Ag9CuS4] with M = Ag, Cu; and T = As, Sb, show a crystal structure which can be described as the succession, along the c axis, of two pseudo-layer modules: a [M6T2S7]2–A module layer and a [Ag9CuS4]2+B module layer. Copper is present in one structural position of the B module layer and replaces Ag in the only fully occupied M position of the A module layer. When the Cu content is >4.00 a.p.f.u., the structural position of the A module layer becomes Cu-dominant and, consequently, the mineral deserves its own name. In this paper we report the crystal-chemical characterization of two Cu-rich members exhibiting the 111 unitcell type (corresponding to the Tac polytype). One sample (space group (P)m1, a 7.3218(8), c 11.8877(13) Å, V 551.90(10) Å3, Z = 1) having As >Sb and with the structural position of the A module layer dominated by Cu, has been named cupropearceite and the other sample (space group (P3̄)m1, a 7.3277(3), c 11.7752(6) Å, V 547.56(8) Å3, Z = 1) having Sb >As has been named cupropolybasite.

Both the new minerals and mineral names have been approved by the IMA-CNMNC.

Synthetic end-member strontium feldspar (SrAl2Si2O8) has been studied in a diamond-anvil cell at elevated pressures up to 10.3 GPa using energy-dispersive X-ray powder diffraction. Cell parameters have been refined between ambient pressure and 6 GPa. SrAl2Si2O8 undergoes a ferroelastic phase transition from the ambient pressure monoclinic space group I2/c to the high-pressure triclinic space group I at 3.2 ± 0.4 GPa. The transition appears to be first-order and the ferroelastic and co-elastic components of the spontaneous strain tensor have been calculated.

Organic molecules control calcite growth byadsorbing preferentiallyonto particular surfaces of the crystal. Adsorption of a monosaccharide (-galactose) on various calcite surfaces has been simulated with molecular dynamics. The calculations of Z-density, mean square displacement (MSD) and adsorption energyindicate that the adsorption of monosaccharide on the acute-stepped calcite (31.8) surface is more favourable than that on the obtuse-stepped (31.16) surface, which suggests that monosaccharides maybe able to selectivelycover some surfaces, inhibit crystal growth on these surfaces, and as a result shape the calcite crystals as seen in biominerals, e.g. coccoliths.

A new mineral glikinite, ideally Zn3O(SO4)2, was found in high-temperature exhalative mineral assemblages in the Arsenatnaya fumarole, Second scoria cone of the Great Tolbachik Fissure Eruption (1975–1976), Tolbachik volcano, Kamchatka Peninsula, Russia. Glikinite is associated closely with langbeinite, lammerite-β, bradaczekite, euchlorine, anhydrite, chalcocyanite and tenorite. It is monoclinic, P21/m, a = 7.298(18), b = 6.588(11), c = 7.840(12) Å, β = 117.15(3)°, V = 335.4(11) Å3 and R1 = 0.046. The eight strongest lines of the powder X-ray diffraction pattern [d in Å (I) (hkl)] are: 6.969(56)(00$\bar{1}$), 3.942(52)(101), 3.483(100)(00$\bar{2}$), 3.294(49)(020), 2.936(43)(120), 2.534(63)(201), 2.501(63)(20$\bar{3}$) and 2.395(86)(02$\bar{2}$). The chemical composition determined by electron-microprobe analysis is (wt.%): ZnO 42.47, CuO 19.50, SO3 39.96, total 101.93. The empirical formula calculated on the basis of O = 9 apfu is Zn2.07Cu0.97S1.98O9 and the simplified formula is Zn3O(SO4)2. Glikinite is a Zn,Cu analogue of synthetic Zn3O(SO4)2. The crystal structure of glikinite is based on OZn4 tetrahedra sharing common corners, thus forming [Zn3O]4+ chains. Sulfate groups interconnect [Zn3O]4+ chains into a 3D framework.

Ankerites from the Northumberland coalfield were first described, with chemical analyses, some ten years ago (Hawkes and Smythe, 1935), when it was found that examples from veins exposed on the coast near Hartley and from sludge from nearby coal-washeries showed a remarkable uniformity in composition. The operations of the collieries concerned cover an area roughly 6 × 6 miles, and range from the Beaumont to the High Main Seam. In order to ascertain whether this uniformity is maintained over a wider area, five additional samples of ankerite from veinlets in rocks of Coal Measure age, and one from partings in the Lower Carboniferous Scremerston coal have been examined. The Coal Measure rocks cut by the veinlets have been proved to contain substantial proportions of ferriferous carbonates, while for comparative purposes two examples of rocks of similar age with carbonate but unaccompanied by ankerite veinlets have been investigated. The range in composition of ankerites in the coalfield has proved to be small.

Significant uncertainty surrounds the processes involved in the formation of basalt-hosted corundum, particularly the role that the mantle plays in corundum generation. Some previous studies have suggested that trace-element ratios (namely, Cr/Ga and Ga/Mg) are useful for distinguishing two types of corundum: ‘magmatic’ and ‘metamorphic’, designations that include mantle and crustal processes. However, recent studies, including this one, have discovered transitional groups between these end-members that are difficult to classify.We used laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) to measure trace-element concentrations in sapphire and ruby crystals from eight alluvial deposits that span a significant length of the eastern Australian gemstone belt. Additionally, we collected LA–ICP–MS U–Pb and traceelement data from zircon megacrysts atWeldborough, Tasmania, which is also within the gemstone belt. Our sapphire and ruby results reveal a continuum in trace-element compositions, an observation that raises questions regarding previous classifications that ascribe corundum from basalt-hosted gemfields to either ‘magmatic’ or ‘metamorphic’ sources. The spatial association of basalt-related gemfields in eastern Australia with a long-lived convergent margin suggests a link between corundum formation and Al-enrichment of the mantle wedge during periods of subduction.

A variety of mushroom tourmaline from the Kat Chay mine, Momeik, near Mogok, Shan state, Myanmar, consists of a black-to-grey single-crystal core from which a single prismatic crystal reaches to the edge of the mushroom, forming a slight protuberance. The rest of the mushroom (∼50% by volume) consists of extremely acicular sub-parallel crystals that diverge toward the edge of the mushroom. The acicular crystals are dominantly colourless to white, with a continuous black zone (2 mm across) near the edge, and pale pink outside the black zone. The composition varies from ∼Na0.75Ca0.05(Li0.80Al0.70Fe1.10.Mn0.30Ti0.10)Al6Si6(B03)3O18(OH)3(OH,F) at the base of the mushroom to ∼Na0.60Ca0.06(Li1.00Al1.98Fe0.02)Al6(Si5.35B0.65)(BO3)3O18(OH)3(OH,F) close to the edge at the top of the mushroom. The principal substitutions are: (1) YLi + YAl -> yFe* + yFe* and (2) TB + yAl -> Si + yFe*, but there are five other minor substitutions that are also operative. There are six significant compositional discontinuities at textural boundaries in the mushroom, suggesting that the changes in habit are driven in part by changes in external variables such as T and P, plus possible involvement of new fluid phases.

Mineralogical, geochemical and isotopic data including K-Ar age determinations are presented for one of the largely unknown, Mesozoic ultramafic (lamproitic) occurrences of the Aldan Shield. Ultramafic, ultrapotassic rocks occur as isolated pipes or as dykes in alkaline complexes as the Yakokut complex. K-Ar dating of phlogopites from different ultramafic dyke rocks of Yakokut give cooling ages of 133.3 ± 1.3 Ma. These rocks generally contain olivine, clinopyroxene, phlogopite and spinel phenocrysts. Olivines are forsterite-rich (Fo86–94) and undeformed, suggesting that they are phenocrysts. The low Ti and Al contents of clinopyroxenes are close to those of lamproites. Phlogopite cores are rich in Al2O3 and TiO2 relative to the rims with two different zonation trends caused by distinct crystallization conditions after emplacement. Spinels are Ti-bearing magnetites and Ti-Al-magnesiochromites with high Cr/(Cr+Al) ratios (> 0.9), indicating their crystallization from a lamproitic melt.

Geochemically, the rocks are ultrabasic — basic with high mg# values, low Ca, Al, Na and strong enrichments of Rb, Ba and K. Their CaO/Al2O3, Zr/Nb or Ba/Sr ratios indicate their lamproitic nature and origin in the subcontinental lithosphere of a depleted mantle source which had undergone metasomatic enrichment. As the rocks all show strong negative Nb anomalies and low Ti, Y and Yb contents, the enrichment is attributed to subduction zone fluids. The Sr-Nd-data (87Sr/86Sr0 0.70573−0.70605 ± 0.00003; ɛNd − 10.2 ± 0.7) indicate the origin by partial melting of a heterogeneous mantle source with relatively low Rb/Sr ratios and an early enrichment. The evolution model comprises a depletion of ‘basaltic elements’, leading to a harzburgitic source which was enriched by an early LREE contribution during the stabilization of the Archaean to Proterozoic Aldan Shield. It is further suggested that the Mesozoic northwesterly directed subduction of the Ochotsk-Chukotsk belt influenced the subcontinental lithosphere underneath the Aldan Shield, leading to the observed subduction-related signature of the Yakokut lamproites.

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.

Sedimentary basins developed along the European margin during the earliest, Permian, stage of proto-Atlantic rifting, during a phase of high heat flow. The proximity of some basins to Caledonian thrusts has implied that rifts locally utilized the basement fabric. New mineralogical and palaeomagnetic data show that thrust planes in the Moine Thrust Zone channelled a pulse of hot fluid in Permian time. The fluids precipitated kaolin in fractures in the thrust zone, and with decreasing intensity away from the zone. The high-temperature polytype dickite is largely confined to major thrust planes. Stable H and O isotope analyses indicate that the parent fluid included meteoric water involved in a hydrothermal system. Coeval hydrothermal hematite has a chemical remanence that dates the fluid pulse as Permian. This is direct evidence for post-orogenic activity in the thrust zone, in which the thrusts vented excess heat during regional crustal extension. The example from the European margin exemplifies the importance of deep-seated structures in the release of heat, and the value of kaolinite polytype mapping as a tool to record anomalous palaeo-heat flow.

Electron-probe analyses and cell dimensions are reported for twenty members of the tapiolite group. The minerals can be placed in ordered and disordered structural groups, the latter with a significantly larger c dimension. The a and c dimensions for both groups are dependent mainly on their titanium contents. The disordered set form part of a discontinuous series through strüverite/ilmenorutile to rutile. The chemical and structural data are incompatible with the existence of ferrotantalite or mossitc as valid species.

Calcite cements from the Lower Cretaceous Avalon zone of the Hibernia field are, in places, extensively recrystallized, which complicates interpretation of the chemical and isotopic data. The oxygen isotopic data are widely scattered with δ18O ranging between +1.6 and −9.2 for calcite and siderite. Siderite has lower δ13C values (−6.6 to −13.2) than calcite +12.4 to −9.8. Typical trace element contents determined by ICP on acid-leached samples, range from 270 to 2100 ppm Sr and 180 to 2200 ppm Zn in calcite.

The trace element data indicate that some of the calcite has been precipitated from, or recrystallized by meteoric water. The trace elements show trends related to variations in δ18O in such a way as to imply that not all the spread to low δ18O values can be attributed to meteoric water influence alone. The data are not well enough constrained to calculate meaningful temperatures, but the range of °18O values probably represents an elevated range of temperatures of precipitation or recrystallization.

Microprobe analyses show that non-recrystallized fossils have a composition distinctly different from veins, cements, and recrystallized fossils, all of which are similar. The compositions of calcite cements are highly variable, with FeO (for example) ranging from 0.15 to 4.39 wt. %, but show no consistent patterns of zonation. Fossil fragments which show no textural evidence of recrystallization have low FeO contents (0.2 wt. %). Meteoric water, believed to be responsible for at least some of the cementation and recrystallization observed, probably entered the Avalon during and after formation of the mid-Cretaceous unconformity.

Monoclinic, non-stoichiometric natrojarosite—hydroniumjarosite solid solution phases have been synthesized hydrothermally over a range of temperatures, starting compositions and reaction times, and have been characterized using Rietveld refinement of synchrotron X-ray diffraction data, and chemical and thermal analyses. The H atom locations have been obtained from refinement of neutron diffraction data on a deuterated sample. The results confirm a direct relationship between the monoclinic distortion and the ordering of iron site vacancies in one of two independent iron sites. Ordering of iron vacancies gives rise to domains containing butlerite-like 7 Å chains of corner-connected octahedra and tetrahedra. The formation of these chains within (100) planes results in an expansion of the monoclinic a lattice parameter and a contraction of the c parameter relative to stoichiometric jarosites. The results support a recent model for iron deficiency, whereby an iron vacancy is compensated by the replacement of four coordinated OH– ions by H2O molecules, with one of the H2O molecules coming from deprotonation of H3O+. The general formula, based on intergrowth of stoichiometric jarosite and non-stoichiometric, butlerite-like regions, is [(Na,H3O)Fe3(SO4)2(OH)6]1–y[(H2O)Fe2(SO4)2(OH)2(H2O)4]y.