The Fountain Hill skarn, which was produced by thermal metamorphism of impure limestone in the Omey Granite aureole, consists of wollastonite, calcite, grossular-andradite garnet, diopside, B-free vesuvianite and small amounts of albite, K-feldspar and quartz. Zoning in vesuvianite is, overall, independent of birefringence but oscillatory concentric zoning in the mineral is controlled mainly by Ti. In addition to extensive within-site substitutions (e.g. F for OH in the OH-sites, Fe2+ for Mg, Fe3+ for Al, Ti for Al etc. in the Y-sites), there are significant cross-site combined substitutions involving Y-X and Y-Z but not X-Z sites so that ideal solution models for this mineral are not applicable. The thermodynamic mole fraction of Hoisch (1985) is modified to account for the excess of the ΣY cations in the Y sites and can be applied to both B-bearing and B-free vesuvianites. Using the thermodynamic dataset of Holland and Powell (1990) and taking into account the existence of andalusite, sillimanite and corundum in associated pelites, leads to the conclusion that the metamorphic conditions were about 640±20°C and 3.3±0.3 kb at 0.15±0.05 XCO2.

The Lavrion area is part of the Attic-Cycladic massif. Blue amphibole analyses revealed that they are glaucophane or ferroglaucophane. Ca-amphiboles are characterized as actinolite or actinolitic hornblende. The Ps component of epidotes from the glaucophane-bearing rocks varies from 25.42–30.89%, whereas the Ps component of epidotes from the greenschist assemblages ranges from 23.81–26.88%. Chlorites show narrow compositional variations of ferromagnesian ratios (Xmg=0.48–0.53). Albites are almost pure Ab100. The Kfeldspar present has a low Ab content. The evolution of the prasinites studied is characterized by the progressive transformation of eclogite facies (?) rocks through epidote blueschists into greenschists. A P-T path for the prasinites is presented indicating epidote blueschist facies at P-T conditions of around 7.0–7.5 kbar and 300–340°C. Pressures of 4.0–4.5 kbar and temperatures around 340–360°C are estimated for the subsequent overprint in the greenschist facies. The path EBS to GS conditions followed under nearly isothermal uplift.

The study focuses on the distribution of B, Be, Li, rare earth elements (REE), high-field-strength elements (HFSE), Th, U and Pb in fresh and hydrothermally altered ocean island basalts (OIB) from French Polynesia, and evaluates B/Be and Li/Be ratios as potential tracers of subducted components in the mantle. Hydrothermal solutions affecting the rocks during cooling were derived from meteoric water, sea water and magmatic fluids. The concentrations of REE, HFSE, Th and Be in the OIB were not affected by secondary processes except during advanced stages of subaerial hydrothermal alteration where saponite was a dominant secondary phase. This alteration modified the contents of these elements, changed REE patterns and produced a positive Ce anomaly. The subaerial and submarine hydrothermal alteration (T ∼ 70–100°C) may change U concentrations in OIB, whereas Pb was only marginally redistributed during alteration.

Boron was enriched during submarine and subaerial hydrothermal alteration but was not noticeably affected in basalts altered by magmatic fluids at T > 200°C. Like B, the mobility of Li during the alteration varies with fluid temperature. Lithium became enriched in the basalts during advanced stages of lower T hydrothermal alteration (<100°C). However, this element was partly removed from the rocks during higher T alteration (>200°C) by magmatic fluids. Boron, Be and Li behave as incompatible trace elements in basaltic magmas. Beryllium content in primitive mantle is estimated to be 0.07 ppm. Fresh Polynesian OIB have low abundances of B and Li and low B/Be (2–5) and Li/Be (2.5–5) ratios compared with volcanic arc rocks, marine sediments and altered oceanic crust. Various OIB including even those which have HIMU- and EM-affinities have similar overlapping B/Be and Li/Be ratios. Both B and Li are probably stripped from a lithospheric slab during subduction-related metamorphism and are, thus, not involved in deep mantle recycling. The mantle-normalized trace element abundances of MORB and OIB usually display patterns characterized by negative B, Pb and Li anomalies. The patterns of continental crust and crustal rocks have distinct positive anomalies for these elements whereas continental basaltic rocks have variable relative abundances of B, Pb and Li. The anomalies of these elements in basalts can be useful in discriminating their tectonic setting and constraining the mantle source regions of basalts.

Several of the Proterozoic natural fission reactors at Oklo, Gabon contain abundant organic matter (bitumen), with which much of the reactor uranium is associated. An understanding of the petrography of the bitumen is important in assessing its role in element retention following fissiogenic reactions. The bitumen is replacive and includes vestiges of detrital grains and clays of the host sandstones. It also contains several generations of mineral phases related to the migration of uranium and daughter lead, and other elements mobilized by hydrothermal activity in the reactor zones. The minerals include (primary) uraninite precipitated after reduction of uranium by organic matter, silicates concentrated in radiation halos around the uraninite, and native lead, galena and further uraninite which migrated from the primary uraninite. The silicates are illitic clays in the immediate vicinity of the reactors, and chloritic more distant from the reactors. Authigenic clays in radiation halos are compositionally distinct from earlier host rock clays. Local migration of uranium and lead is evident as dispersion of the elements through the radiation halos; cross-cutting veinlets of uraninite, native lead and galena, including veinlets extending directly from the primary uraninite crystals; and concentrations of the elements at the margins of bitumen masses. The limit of observed uranium dispersion is within clay immediately beyond the bitumen margins.

Silicate minerals grown from glasses, and rapidly cooled melts, often have non-compact branching or ‘spherulitic’ morphology. The branching patterns are observed in volcanic rocks, glasses, meteorites, slags and sometimes in shallow level intrusive rocks. Experiments, observations, theory and simulations all support the concept that the crystal morphology is the result of growth under diffusion limited conditions. We show that in a silicate melt under appropriate conditions the equations for heat transfer and chemical-diffusion reduce to the Laplace equation. This means that the temperature or chemical gradient is a steady state field. Interaction between this field and a random variable (Brownian motion of growth species) is modelled and yields complex branching objects. The growing cluster affects the field such that an in-filled structure cannot be formed. The branching structures of the model crystal are remarkably similar to those formed in nature, and to those produced in laboratory experiments, implying that the model captures the essence of the branching-growth process.

A natural Mg-Al-Fe spinel from the Balmuccia peridotite (Italian Western Alps) was annealed at T between 650 and 1150°C, under controlled oxygen activity, and quenched in H2O. Twenty-three cation distributions were calculated from XRD structural refinements in tandem with microprobe analysis, and verified by Mössbauer spectroscopy in the case of unheated samples.

Unheated crystals showed essentially ordered distribution of Fe3+ in octahedral and Fe2+ in tetrahedral sites, the only intracrystalline disorder being represented by ∼0.12 atoms per formula unit of [4]Al and [6]Mg. Thermal runs and quenching maintained substantially ordered distribution of Fe2+ and Fe3+ up to ∼990°C and produced continuous [4]Mg-[6]Al exchange. Between 990 and 1150°C, the previous order of Fe2+-Fe3+ appeared to change slightly, [6]Fe2+ reaching ∼0.04 afu and [6]Mg ≅ [4]Al ≅ 0.24 afu at the highest T. After quenching from this temperature, Fe2+ still resided mainly in the T site. Some previously heated crystals underwent reordering on lowering of the temperature.

Experimental data, integrated with existing literature, enabled cation-oxygen distance in this structure to be improved. Results from annealed samples allowed the formulation of an experimental thermometric function based on Mg-Al intracrystalline disorder.

Transmission electron microscopy (TEM) was used to study the aluminate sodalite, Ca8[Al12O24](CrO4)2. This aluminate sodalite has four polymorphs: one cubic, one modulated, one tetragonal, and an orthorhombic cell that arise from ordering of [Ca4·CrO4]6+ clusters that occur in the cages of the structure. The transition temperatures are 432, 453, and 610 K. The cell parameters for the orthorhombic phase, with the cubic cell parameter of a = b = c = 9.222 Å, are 3a × 2b × c. Transformation twins are formed at 432 K during the transition from the tetragonal to the orthorhombic phase. The twin plane is {110} in the cubic cell, and {320} in the orthorhombic cell.

Ruby-sapphire-sapphirine-spinel forms small, corroded, crystalline aggregates in corundum bearing alluvials shed from the Tertiary Barrington basalt shield volcano. Sapphirine is near a 7:9:3 (MgO-Al2O3-SiO2) composition and, together with the corundum, shows reaction rims of pleonaste spinel. Spinel in the aggregates has a compositional range Sp 68–73 Hc 27–29 Cm 0–3. The aggregates give new insights into the ruby-sapphire source rocks. Potential origins include metamorphic recrystallization of aluminous material (below 1460°C) or high temperature-high pressure crystallization reactions related to lamprophyric or basaltic magmas (up to 1300°C and 20 kbar). Sapphirine-spinel thermometry suggests final crystallization temperatures for the aggregates around 780 to 940°C and reaction with host magmas at over 1000°C.

The Barrington gemfield includes two distinct corundum suites. One, typical in eastern Australia, is dominated by blue-green, well-crystallized, growth-zoned sapphire, commonly containing rutile silk and Ferich spinel inclusions (Hc 51–73, Mt 18–35, Mf 6–8, Usp 2–6). The other, an unusual suite, is dominated by ruby and pastel coloured sapphires, with little crystal shape or growth zonation and restricted mineral inclusions, mostly chromian pleonaste and pleonaste. The ruby-sapphire-sapphirine-spinel aggregates provoke new thoughts on the origin of rubies and sapphires and their indicator minerals in eastern Australian and southeastern Asian volcanic gemfields.

The compositions and textural relationships of the oxide minerals zirconolite, pyrochlore and baddeleyite are described. These occur as accessory minerals, often intergrown with each other, from a phoscorite rock associated with the Kovdor carbonatite complex. Both the zirconolite and baddeleyite have relatively high concentrations of Nb and Ta; the pyrochlore is rich in U and Ta. Backscattered electron images, coupled with detailed microprobe analyses, reveal complex compositional zoning in zirconolite and pyrochlore which reflect changes in the fluid composition during growth of these minerals. A comparison is made of incompatible element ratios Zr/Hf, Nb/Ta and Th/U between the three accessory minerals.

Ferrous substituted saléeite is a new variety of saléeite from Arcu su Linnarbu, Sardinia. It is tetragonal with a = 6.982(2) c = 19.660(2) Å, Z = 2; the ideal formula is (Mg,Fe2+)(UO2)2(PO4)2·4H2O. The strongest lines in the X-ray powder diffraction pattern are: 3.473(100)(114), 4.95(50)(110), 4.91(40)(004), 4.443(40)(112), 2.200(30)(118), 2.193(30)(303) and 2.178(30)(009). The mineral is light-yellow in colour and is dull fluorescent. The measured density is 3.242 g/cm3 and Z = 2. There is a prominent (001) cleavage. Refractive indices are : α = 1.572(2) β = 1.577(2) γ = 1.581(2) and 2V = 48°(2). The pleochroism is very weak and the elongation is positive parallel to Y. The mineral occurs as subparallel crystal aggregates with a quadratic outline.

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 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).

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).

Spontaneous fission reactions occurred in several uranium deposits in SE Gabon approximately two billion years ago. The reactor zones, between 10 to 50 cm thick, are found in Proterozoic sandstones and consist of high-grade uranium ore mantled by illite and/or chlorite (Gauthier-Lafaye et al., 1989). During a mineralogical study of sandstones (quartz arenites) underlying a natural fission reactor at Bangombé (20 km south of the Oklo uranium deposit), we have found several grains of a uranous silicate, coffinite, with unusually high concentrations of phosphorous and enriched in light rare earth elements (LREE).

Guidelines on mineral nomenclature published by the Commission on New Minerals and Mineral Names (CNMMN) of the International Mineralogical Association (Nickel and Mandarino, 1988) include the following statement: "If an artificial substance has been given a name, and a mineral corresponding to that substance is subsequently discovered, the name given to the artificial substance does not necessarily have to be applied to the mineral".