Three voluminous Quaternary phonolitic pumice fall deposits erupted from the compositionally-zoned Tenerife magma chamber exhibit variability in Sr and Pb isotope ratios. It has been previously argued that the Sr isotope variations are due to syn-eruptive interaction between magma and hydrothermal fluids (Palacz and Wolff, 1989). Pb compositions are not correlated with Sr, and are believed to reflect magmatic values. Pb isotope ratios exhibit regular variation with degree of fractionation, and one zoned deposit is heterogeneous in Pb. The highest values seem to characterize the most fractionated upper parts of the zoned system. This is unlikely to be a consequence of magmatic recharge. Isotopic and trace element behaviour is instead consistent with combined assimilation and fractional crystalliza- tion, involving the recycling of material containing relatively radiogenic Pb, from within the volcanic edifice. Assimilation of sediment intercalated within the submarine portion of the pile is ruled out by the isotopic data. The most probable contaminant is a felsic igneous rock. Early trachytes reported by Sun (1980) have the required Pb isotope compositions and may approximately represent the assimilant.

An apparatus is described for the measurement of the rates of fast precipitation reactions. It consists of a T-tube, where reactants are added to the arms of the T, mixed rapidly at the junction, and the rates of disappearance of reactants or appearance of products are measured along the stem of the T. The geometry of the system results in a steady state being established in the apparatus, enabling detailed analysis of reaction progress. The apparatus has been used to investigate the kinetics and mechanism of iron sulphide precipitation reactions. It has enabled measurements to be made with relatively high precision and good accuracy of the first 130 ms of reaction time.

The new mineral bernardite has been identified on one specimen from Allchar, Macedonia, Yugoslavia, together with orpiment and realgar. It forms black crystals, the size of which may exceed 1 mm. The streak is deep red; on an arbitrarily oriented section R(589nm) ranges from 23.8 to 24.7% in air, from 10.2 to 11.6% in oil. Microprobe analyses together with an X-ray structure analysis suggest the ideal formula TlAs5S8, with a possible replacement of As by Sb up to 15 wt. %. Monoclinic; a 15.647(4), b 8.038(3), c 10.750(3) Å, β 91.27(3)°; space group P21/c; Z = 4; R = 0.049, wR = 0.036 for 2410 reflections. The atomic arrangement consists of a 3-dimensional As5S8 framework with eight-coordinated T1 in its holes. The mineral is named for Doc. Dr Jan H. Bernard, Prague, Czechoslovakia.

Mineral and fluid inclusions were studied in seven gem corundums from gravels of three areas in Sri Lanka. All fluid inclusions are pure CO2. Microthermometry results on primary fluid inclusions suggest formation of corundum under granulite facies metamorphism (>630°C, 5.5 kbar). Secondary fluid inclusions indicate different retrograde events of post-metamorphic cooling and uplift for different source areas.

Saddle dolomite is a common product of late-stage diagenesis and hydrothermal activity. It has been suggested that during growth Ca enrichment occurs towards crystal edges leading to a lattice expansion relative to face centres. However, backscatter scanning electron microscopy of eight samples has revealed that, instead of edge associated Ca enrichment, saddle dolomites have a series of edge associated Mg enriched wedges, between 5 and 20 µm thick and 300 µm long. Wedge geometry implies development of extra lattice layers at edges relative to face centres. It is suggested that the wedges develop during rapid, transport-controlled, crystal growth. The wedges possibly reflect a switching from continuous growth across the face to edge-nucleated growth as the boundary layer solution becomes progressively depleted. Continuous growth might be reinstigated through convective turnover of the boundary layer presenting fresh solution to the growing crystal.

Strictly reproducible syntheses of the trimorphs of composition Cu2Cl(OH)3, atacamite, paratacamite, and botallackite, have been developed. In syntheses involving direct precipitation, or reaction of aqueous solutions with solid phases, reliable results are obtained only if the temperature and time of reaction are carefully controlled. Botallackite, the rarest of the naturally occurring trimorphs, is a key intermediate and crystallizes first under most conditions; subsequent recrystallization of this phase to atacamite or paratacamite, or of the latter from the former, depends upon the precise nature of the reaction medium. The crystallization sequence indicates that paratacamite, as has long been suspected, is the thermodynamically stable phase at ambient temperatures. Spertiniite, Cu(OH)2, can be reproducibly synthesized via one route in the non-commutative titration of aqueous copper chloride with aqueous sodium hydroxide solutions.

The nomenclature of CaZrTi2O7 minerals has become very confused, such that zirconolite, zirkelite and polymignite each have acquired multiple meanings and represent five different crystal structures. To resolve these inconsistencies, the IMA approved resolutions as follows. Zirconolite is the non- crystalline (metamict) mineral or mineral with undetermined polytypoid of CaZrTi2O7. Zirconolite-3O is the three-layered orthorhombic polytypoid of CaZrTi2O7. Zirconolite-3T is the three-layered trigonal polytypoid of CaZrTi2O7. Zirconolite-2M is the two-layered monoclinic polytypoid of CaZrTi2O7. Polymignite (metamict) is discarded as equivalent to zirconolite. Zirkelite is the cubic mineral with formula (Ti,Ca,Zr)O2−x.

Manganotantalite replacement by (1) microlite and (2) ferrotantalite, and changes in composition of uranoan microlite from rare-metal pegmatites in South Africa and Namibia have been investigated with the electron microprobe. A uranmicrolite from Karibib, Namibia contained 14.35% UO2, 1.03% PbO, 56.12% Ta2O5, 13.18% Nb2O5, 0.58% Fe2O3, 6.87% CaO, 0.54% SrO, 0.59% MnO, 0.86% Na2O and 0.47% F. Analyses along traverses across a 1.3 mm uranoan microlite, Tantalite Valley, Namibia, revealed two essentially distinct compositions: a more hydrated rim area of 200 µm radius containing 7% higher Ta2O5, 10% lower CaO and 1.3% lower F than a main central area of slightly variable composition. Back-scattered electron images reveal zoning and distinctive subspheroidal structures. New data and structural features are given for radioactive uranoan microlite from Namaqualand, South Africa. These crystals contain remnants of a bismuth phase and are in various stages of replacement. In the microlites replacing manganotantalite, the microlite reflects the composition of the replaced mineral. At Rubicon Mine, Karibib, a narrow marginal zone of mangantantalite is replaced by ferrotantalite along cleavages; a zone of intermediate composition is apparent. Detailed traverses have been completed across all of these crystals.

Yellow blades on joint surfaces in granite from Merrivale quarry, Dartmoor, Devon, are shown to be of a slightly aresenatian variety of phurcalite by X-ray powder diffraction, infrared spectroscopy, electron microprobe and thermal analyses and optical methods. The results from these techniques are tabulated, including assignments for infrared absorption bands. Comparison of X-ray powder diffraction, infrared spectroscopic and optical data with those obtained from samples of ‘nisaite’, an incompletely described mineral from Nisa, Portugal, indicates that the latter is also phurcalite.

The coupled thermal oxidation and deprotonation in air of iron-rich biotite (FeO + Fe2O3 = 34%) has been investigated by EXAFS and XANES spectroscopy at the Fe-K edge and by XANES spectroscopy at the Ti-K edge. Samples annealed for 5 h at temperatures between 250° to 600°C have been studied. Distortions mainly of the Fe-Fe correlation within the octahedral layers are reflected in increasing Debye-Waller factors of the Fe-Fe correlation peak proportional to the annealing temperature. Unchanged Fe-O nearest-neighbour and Fe-Fe next-nearest-neighbour coordination numbers show that these distortions, nonetheless, do not change the structural topology of the octahedral layers. A model is introduced to demonstrate that increasing distortions are compatible with the expected heterogenous deprotonation mechanism in biotite. Titanium occurs in octahedral coordination. It was found to be unaffected by the coupled oxidation/deprotonation process. Both the coordination number and the valence state stay constant during the annealing process, in spite of dramatic changes of the Fe2+/Fe3+ ratio. Thermally activated hopping conduction involving Ti according to Fe2+Ti4+ → Fe3+Ti3+ is, therefore, not a significant process during thermal deprotonation and oxidation in biotite.

Deerite has been found in layers of Fe-rich metasediments, metamorphosed under conditions of blueschist to eclogite facies (T = ca. 480°C). Geochemical comparisons with other deerites described in the literature show that the Ile de Groix deerites most closely resemble the Mn-poor, alpine type, and Sifnos deerites. The P-T conditions of the Ile de Groix metamorphism do not conform with the stability field of deerite. In the assemblages examined here deerite seems to be a relic from earlier stages of prograde metamorphism.

In the Gåsborn area, West Bergslagen, central Sweden, Mn-silicate-magnetite-jacobsite skarns were formed as the result of three successive processes. (1) Deposition of exhalative-sedimentary manganiferous iron-ore-bearing sediments together with cherts and volcanics. (2) Intrusion of a synvolcanic anorogenic granite and some slightly younger gabbros and tonalites: under influence of these intrusives the manganiferous iron-ore-bearing sediments were metamorphosed into (a) rhodonite(I)-magnetite-pyrophanite-garnet assemblages; (b) (manganiferous) hedenbergite(I)-allanite-titanite-garnet-magnetite assemblages; (c) tephroite-jacobsite-pyrophanite-garnet assemblages and (d) magnetite-bearing quartzites. (3) Release of hydrothermal fluids from the granite and subsequent alteration of the above assemblages into metasomatic infiltration skarns, consisting of rhodonite(II), garnet, hedenbergite(II), biotite, actinolite or edenite (with up to 20.11 wt.% MnO), chlorite, bementite, fluorite, helvite, rhodochrosite, hematite, rutile and accessory galena, sphalerite, wittichenite, aikinite, pyrrhotite, chalcopyrite and pyrite.

The maximum temperature (T) and pressure (P) during contact metamorphism are estimated at 550°C and 1.0 kbar respectively. The fluid under influence of which the metasomatic infiltration skarns were formed was relatively rich in Fe, Cl and F and carried little or no Mg and Mn.

During early diagenesis (beginning of stage 2) fo2 was between the hematite/magnetite (hm/mt) and the hausmannite + hematite = jacobsite buffers (h + m = j). During stage 2, with increasing T, fo2 changed from above to below hm/mt. Magnetite and jacobsite at some distance from the hydrothermal veins from which the metasomatic skarn-forming fluids were released, were altered during stage 3 into hematite. Magnetite in, and close to the hydrothermal veins was not altered to hematite, implying an increase in fo2 to above hm/mt with increasing distance from these veins.

The crystal structure of a Mn-bearing kilchoanite, Ca2.33Mn0.67Si2O7, orthorhombic, I2cm, a = 11.356(2), b = 5.007(1), c = 21.817(1)Å, Z = 8, was refined using single-crystal X-ray data to an R value of 3.1% for 1725 unique reflections. It is isostructural with kilchoanite, Ca3Si2O7, and shows a partial disorder of Mn and Ca over the four octahedral sites. On a basis of occupancy refinement, the M3 site (〈M3-O〉 = 2.307 Å) contains 0.508Ca and 0.492Mn, and the M4 site (〈M4-O〉 = 2.346 Å) contains 0.822Ca and 0.178Mn, whereas the M1 and M2 sites (〈M1-O〉 = 2.538 Å, (〈M2-O〉 = 2.380 Å) are occupied only by Ca. Substitution of Mn cations for Ca can be interpreted as taking place on the following sites in preferential order: (1) the smaller Ca site; (2) the less distorted Ca site; (3) the Ca site showing a loss in neutrality of formal electrostatic valence. A statistical survey of Si-O-Si angles observed in silicates containing [Si2O7] groups confirms that these angles become smaller with an increase in the coordination number of the bridging oxygen. Oversaturation of electrostatic bond-strength to the bridging oxygen in some groups of the crystal structures with two tetrahedra sharing a vertex (pyro-anion, ), which is caused by increase in the coordination number of the bridging oxygen and/or by T cations with larger charge than 4+, results in longer T-Obr bonds length and in smaller T-Obr-T angles.