Phosphorus contents in cumulus rocks occurring close to the level of apatite appearance in the basic rocks of the Bushveld Complex, South Africa, provide a method of calculating the proportion of intercumulus component in these rocks. Previous experimental studies have accurately constrained the phosphorus content of magmas when apatite becomes stable. The ratio of the phosphorus content in the cumulates immediately below the appearance of apatite to this liquid composition defines the proportion of trapped liquid.

Application of this method to rocks from the uppermost mafic rocks of the Bushveld Complex leads to the conclusion that there is from 1 to 6 per cent intercumulus component. Many of these rocks are multiphase cumulates and in such rocks estimation of intercumulus component from textural criteria is difficult.

If crystals grow In situ on the floor of the magma chamber such small proportions of interstitial component can be produced without appealing to excessive diffusion and circulation of magma through an unconsolidated crystal pile. The geometry of the intrusion as well as its size might have a major influence on the proportion of the liquid ultimately solidifying within a cumulus rock.

Zeolites K-F and W (EDI and MER types) were synthesized hydrothermally using a natural rock as raw material. Chemical treatments were carried out on a diatomitic rock (containing opaline silica) from Crotone (Calabria, Italy) in order to separate/obtain potassium silicate, a reagent necessary for synthesizing zeolites. Synthesis experiments were performed by mixing the obtained siliceous solution with potassium hydroxide and alumina in varying proportions at 150°C and room pressure. Four synthesis series were performed to form zeolite K-F (EDI) and zeolite W (MER).

The chemical-physical and morphological characterization of the zeolite phases were carried out. Cell parameters were calculated using the Rietveld method. Infrared, thermal and nuclear magnetic resonance (29Si) experiments confirmed the high quality of the zeolite products. The amorphous phase in the synthesis powders was estimated with quantitative phase analysis using the combined Rietveld and reference intensity ratio methods.

X-ray, density, refractive index, and optical absorption measurements have been made on metamict Ceylon zircons. The appearance of a previously reported anomalous optical absorption spectrum in low Ceylon zircons has been associated with small particles of cubic or tetragonal zirconium dioxide in a radiation-damaged zircon lattice, in both heated and unheated stones. No evidence of a previously reported second phase was detected in intermediate Ceylon zircons.

The chemical formula of fiedlerite, a rare hydrated lead halide, has been revised. The mineral is now known to contain also fluorine, and the new, correct formula is Pb3Cl4F(OH)·H2O. X-ray diffraction studies on fiedlerite from Laurion, Greece (the type locality), and from Baratti, Italy (the second known occurrence), revealed its Order-Disorder (OD) character. All structures within this OD family can be built up by layers of the same kind. The two polytypes with Maximum Degree of Order (MDO) display triclinic and monoclinic symmetry, with one and two OD layers, respectively, in the unit cell. On these grounds the nomenclature of fiedlerite has been revised, and the mineral is designated together with the polytype suffix (i.e. fiedlerite-1A, fiedlerite-2M). The crystal structures of the two MDO polytypes of fiedlerite have been solved and refined: fiedlerite-1A: P, a = 8.574(3) Å, b = 8.045(4), c = 7.276(2), α = 89.96(4)° β = 102.05(4), γ = 103.45(4), R = 0.092; fiedlerite-2M: P21/a, a = 16.681(4) Å, b = 8.043(3), c = 7.281(2), β = 102.56(4)°, R = 0.061. In both structures Pb is eight-coordinated by different ligands [CI−, F−, (OH)−, H2O] that define bicapped trigonal prisms.

Two crystals from a sample of titanite from the Heftetjern granitic pegmatite, Tørdal, southern Norway, were extracted for structure analysis and shown to have triclinic symmetry. Unit-cell parameters are as follows: a = 7.0696(4) Å, b = 8.7167(5) Å, c = 6.5695(3) Å, α = 89.7372(11)°, β = 113.7607(10)°, γ = 90.2929(13)°, V = 370.52(6) Å3 for one crystal and a = 7.0612(5) Å, b = 8.7102(6) Å, c = 6.5628(4) Å, α = 89.7804(16)°, β = 113.7713(13)°, γ = 90.2502(16)°, V = 369.39(7) Å3 for the other. The interaxial angles α and γ deviate from the value of 90° required for monoclinic symmetry by ~200–250 standard deviations. The single-crystal X-ray intensities were averaged in both monoclinic and triclinic Laue symmetries, giving R(merge) values of ~14% and ~1.3% respectively. For both crystals, more than 50 reflections with I > 3σI violated the criterion for the presence of the a-glide required for monoclinic A2/a symmetry. Both crystals were refined in the space group A with Z = 4, and final R1 indices are 4.4% and 4.7% (wR2 = 8.4 and 8.9%) respectively. The composition of one crystal was determined by electron microprobe analysis: Ca[Ti0.623Ta0.105Nb0.018Al0.137Fe0.0463+Sn0.0834+]Σ=1.012(SiO4)O. The characteristic corner-sharing [MO5] chains of identical octahedra observed in monoclinic titanite become chains of alternating M(1) and M(2) octahedra of different size, with the stronger X-ray scattering constituents concentrated at the M(2) site. Short-range bond-valence considerations suggest that the M cations will order as Al—O—Ta in adjacent octahedra, and when present in sufficient amounts, will couple along the chain to break long-range monoclinic symmetry.

The Hällefors silver deposit is regarded as a volcanogenic-exhalative iron ore deposit with dispersed amounts of Ag-Pb-Zn (±Cu) which has undergone secondary remobilization leading to the concentration of sulphides and sulphosalts. Based on data from the iron oxides and sulphides, the sulphide-sulphosalt mineralization is believed to have been formed in two stages. The first is characterized by the ranges 573-473 K and 2.25–1.5 kbar, higher gradient of changes of log aS2 with temperature and mostly sulphide precipitation; the second by the ranges 473–443 K, lower gradient of changes of log aS2 and mainly sulphosalt deposition. Assuming the precipitation was from fluids and aqueous solutions, possible conditions of formation of some of the iron minerals have been determined.

The fusion crusts of meteorites form due to heating during atmospheric entry and have mineralogies which are strongly influenced by changes in oxidation state. We have studied the fusion crusts of the most reduced primitive meteorite group, the enstatite chondrites, since they should demonstrate pronounced changes on oxidation. The fusion crusts are dominated by highly unequilibrated assemblages of sulphide, metal and oxide with compositions indicative of progressive oxidation by the reaction with atmospheric oxygen. Troilite becomes depleted in Ti, Cr and Mn, and enriched in Ni with increasing oxidation. Enrichments in the Ni-contents of kamacite and depletions in Si-content also occur with oxidation, although contemporaneous enrichments in Si within metal droplets occurs by partial melting. Assemblages dominated by Fe-oxide are found within fusion crusts as reaction rims on metal, as veins and within troilite-metal assemblages as droplets and formed by oxidation of metal during heating. Despite the evidence for large increases in redox state during heating, fusion crusts also contain lithophile sulphides indicating a high degree of disequilibrium during the atmospheric reprocessing of enstatite chondrite materials. Based on comparisons with experimental phase relations, ablation rates of 0.08–0.25 cm s−1 are predicted from the thermal gradients recorded in fusion crusts; these rates are broadly similar to those suggested for other meteorite groups.

Mountkeithite [(Mg,Ni)9(Fe3+,Cr,Al)3(OH)24]3+[(CO{in3,SO4)1.5(Mg,Ni)2(SO4)2(H2O)11]3− occurs with pyrite, magnetite, magnesite, hexahydrite, and morenosite in a low-temperature hydrothermal vein system in the Mount Keith disseminated nickel sulphide deposit, Western Australia. Electron-microprobe analyses gave the following average composition: MgO 31.7, NiO 6.1, CuO 0.1, Cr2O3 6.1, Fe2O3 8.3, Al2O3 2.6, SO3 14.7; microanalysis for C and H gave CO2 3.9, H2O 30.6; total 104.1. The X-ray powder diffraction pattern has the following strongest lines: 11.30(10), 5.63(8), 4.63(2), 3.765(6), 2.645(4), 2.545(4), 1.554(5), and 1.505(3); these can be indexed on a hexagonal cell with a = 10.698 Å, c = 22.545 Å.

Mountkeithite occurs as friable aggregates and rosettes composed of soft, pearly to translucent, pale pink to white flakes with perfect basal cleavage. Optical properties are uniaxial negative with ɛ = 1.51 and ω = 1.52; weakly dichroic from colourless to palest pink. Specific gravity is 2.12 (calc. 1.95). Mountkeithite is soluble, with efferves-cence, in dilute HCl. Mountkeithite changes to a pyroaurite-like phase, with a 7.8.Å basal spacing when immersed in water, but can be changed back to an 11.3 Å phase by immersion in 1M MgSO4; mountkeithite also collapses to a 7.8 Å basal spacing under vacuum. Phases similar to mountkeithite have been synthesized by immersing grains of stichtite in 1M MgSO4, at 20, 50, 105, and 200°C.

The structure of mountkeithite is interpreted as consisting of positively charged brucite-like hydroxyl layers, containing both divalent and trivalent cations, separated by about 7 Å-thick, negatively charged interlayers containing carbonate and sulphate anions, magnesium sulphate, and water. Carrboydite, motukoreaite, and hydrohonessite are minerals with similarly large basal spacings of 10–11 Å, and are also believed to have pyroaurite-related structures with expanded interlayers.

Ore specimens from the abandoned copper mine at Seathwaite Tarn, Cumbria, were studied in polished section by reflected light microscopy. The mineral paragenesis is described and related to current views on Lake District ore genesis. A common origin with the neighbouring deposit at Coniston is proposed. Wittichenite was identified in the ore, and is the first authenticated occurrence in Great Britain.

Green biotite-like material occurring in Haast Schist at Brighton, eastern Otago, consists of biotite and a kaolin-group mineral interlayered on a 1 μm scale. Electron probe analyses of composite grains show K2O contents of 4.4 to 8.5 wt.%, in part reflecting the kaolin content, and in part, leaching of K+ ions. Phengitic muscovite shows similar but less extreme effects. Kaolin, siderite, calcite, and titanium oxides have formed in the rock during hydrothermal alteration of epidote, sphene, and biotite by carbonated waters. Potassium leaching due to surficial weathering processes appears to be widespread in biotites from the schists of eastern Otago, and biotites (hydrobiotites?) with K2O as low as 4 wt. % are reported. Similar material with 0.8 to 2.4% K2O and with Na2O about 1% is thought to be more highly degraded biotite. Microprobe analyses of kaolin and chlorites from associated rocks are given in addition to those of ‘biotite’ and phengitic muscovite. Analyses of sheet biotite and sheet muscovite from the Mataketake Range pegmatites in the highest grade parts of the Haast Schist terrane are presented for comparison. The study shows that biotite is more widespread in eastern Otago than was previously thought, and that almandine-rich garnet is not confirmed down-grade of the first appearance of biotite in eastern Otago.

Zincian högbomite (ZnO 3.5–10.5wt.%) occurs as an accessory phase in garnet quartzite that is intimately associated with the Broken Hill and Black Mountain Cu-Pb-Zn-Ag deposits, Aggeneys, South Africa. Högbomite coexists with a number of minerals including quartz, gahnite, sillimanite, sphalerite, pyrrhotine, pyrite, magnetite, and ilmenite, suggesting that högbomite may have formed by sulphidation and oxidation reactions. Such reactions may account for the high Zn content of högbomite. Where associated with metamorphosed massive sulphide deposits högbomite is enriched in Zn relative to that found in ultramafics, Fe-Ti deposits, Fe ores, aluminous metasediments, and skarns. This enrichment in högbomite constitutes a potential exploration guide for metamorphosed massive sulphide deposits.

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.

An occurrence of a celadonite-like mineral in a weathered basalt in the Lake District has been investigated by X-ray diffraction, X-ray fluorescence, electron microprobe, and infra-red spectroscopic methods. The bulk composition of the mineral corresponds to an aluminous-glauconite. The data show that the mineral is most probably a celadonite-muscovite or celadonite-illite mixture, although a celadonite-phengite cannot be entirely discounted. Approximately 10% smectite layers are also present. The results suggest that re-examination of many aluminous glauconites may show them to be mixtures of this type.