The cause of coloration of Blue John fluorite from Castleton, Derbyshire, and blue banded fluorites from Ashover, Derbyshire, and Weardale, Co. Durham, has been investigated by a number of techniques, including mass spectrometry, optical spectroscopy, and paramagnetic resonance measurements on natural and irradiated samples. In all respects Blue John is indistinguishable from the other blue banded fluorites. Although traces of hydrocarbons were found in all the natural fluorites including Blue John, they are shown not to be the cause of the colouration. The optical spectra and bleaching behaviour are consistent with colouration by colloidal calcium rather than F-centres. The causes of colour banding are discussed.

This paper gives a revision and expansion of an earlier interpretation of the thermal expansion behaviour of the framework silicates. The partially-collapsed and ideal fully-expanded structures of quartz, cristobalite, and sodalite are characterized by the geometric relationship between the angle of rotation of their tetrahedra from the ideal fully-expanded state, their cell parameters, and the length of the tetrahedron edge. Their thermal expansion behaviour is interpreted as due mainly to the effect of the rotation of the tetrahedra towards the fully-expanded state modified by anisotropic thermal motion of the framework oxygens and distortion of the tetrahedra from a regular form. With the leucite and sodalite groups the significance of the interframework cations is discussed.

Piemontite-bearing metachert horizons are recorded from regionally metamorphosed eugeosynclinal rocks at Haast River, in the Southern Alps of New Zealand. Piemontite schist mineralogical assemblages produced by epidote-amphibole facies metamorphism are described petro-graphically, and are compared with lower grade occurrences in the Haast Schist Group.

A chemical analysis yields a composition of (Ca1·75Mg0·02Mn0·25Na0·03K0·01) (Al2·23Fe0·53Mn0·24 Ti0·01)Si3·06O12(OH)0·9, which is compared graphically with other metamorphic, hydrothermal, and metasomatic piemontites.

Single-crystal Weissenberg and powder camera X-ray data are given, and an attempt made to relate these X-ray parameters to chemical variation within the piemontite composition range.

Sitathali is an olivine-bronzite chondrite, consisting largely of olivine (Fa18) and orthopyroxene (Fs19) with minor amounts of a clinopyroxene (Ca36Fe12Mg52), plagioclase (An12), nickel-iron, troilite, chromite, and a phosphate (apatite or merrillite). The chemical analysis of a 4 gm sample gave SiO2 39·85, TiO2 0·10, Al2O3 2·84, Cr2O3 0·35, FeO 13·27, MnO 0·28, MgO 23·01, CaO 1·84, Na2O 0·65, K2O 0·15, H2O+ 0·23, H2O− 0·05, P2O5 0·25, FeS 5·09, Fe 10·22, Ni 1·58, Co tr. total 99·76. The metal displays Neumann bands, some deformed, as well as areas of apparent flowage. Troilite locally exhibits twin lamellae and in places replaces kamacite in the plessite fields. Elsewhere it is in braided veinlets and globules, both reflecting former melting. The varied textures suggest a complex post-formational history encompassing several deformational events presumably due to breakups and possible extraterrestrial impacts.

Large samples of the hexahedrites Scottsville, Indian Valley, Okano, Puripica, and Hex River Mountains from the British Museum Collection and a sample of Lombard have been prepared for metallographic examination and details of their structures have been mapped with the aid of a specially constructed X-Y plotting device that is geared to the stage of a metallurgical microscope. The following elements of structure have been studied and an attempt has been made to discuss the circumstances under which they were formed: clear etching and frosty etching kamacite, decorated Neumann lines, giant rhabdites, plate rhabdites, rhabdite clusters, microrhabdites, cohenite or decomposed cohenite, and troilite (which in some instances is recrystallized or remelted). In general the range of structural effects is similar to that previously reported for the Angra dos Reis hexahedrite (Min. Mag. 1971, 38, 94–101). The variations of structure are discussed in relation to nickel content and trace element chemistry of the meteorites.

The one-atmosphere experimental melting and crystallization relations of some basic lavas of Réunion Island, Indian Ocean, are investigated. They comprise products of the extinct volcano Piton des Neiges and the active volcano Piton de la Fournaise. New data and interpretations are presented for the 1939 oceanite and its contained glass, originally described by Lacroix (1939a). The liquidus v. iron enrichment curves for these Réunion lavas fall about 20 °C above those of the lavas of Kilauea, Hawaii. The primitive liquid reaching the surface contained about 10 % MgO.

The Ergheo meteorite was inspected both by transmitted and reflected light in order to look for evidence of shock metamorphism by petrological observations. The stone is a well-recrystallized olivine-hypersthene chondrite that shows features of severe fracturing, prominent veining, and diffused cracking. The presence of several shock-transformed components is described in some detail. Ergheo is a meteorite that suffered particularly by shock in full agreement with Heymann's (1967) and Turner's (1968) statements.

Green calcium sulphosilicate layers were formed in lime-larnite-calcite wall coating in a lime kiln at Rivervale, Western Australia. The compound formed in the kiln flame area by the combination of siliceous lime sand feed with sulphur trioxide from the sulphurous oil fuel.

The calcium sulphosilicate is orthorhombic with a 10·183, b 15·408, c 6·825 Å, space group Pcmn. Crystals are [100] tablets or prisms elongated along c, D 2·95, hardness 5, streak pale green, decomposed by organic acids. Optical properties α 1·632 = [001] blue, β 1·638 = [100] yellow-green γ 1·640 yellow-green, 2Vα = 60°, dispersion r > v, X-ray powder lines: 2·855 (10) 032,202; 2·838 (7) 330,321; 3·35 (6) 012; 2·622 (6) 331; 2·571 (6) 060; 3·20 (5) 231; 1·962 (5); 1·899 (5); 1·896 (5); 1·372 (5).

Chemical analysis by P. Hewson gave: SiO2 21·50, Al2O3 1·83, Fe2O2 0·50, CO2 0·49, P2O5 0·23, CaO 57·19, MgO 0·35, Na2O 0·22, K2O 0·22, SrO 0·15, Li2O 0·06, SO3 16·71, H2O+ 0·28, H2O− 0·10, others 0·04, total 99·87. On a water-free basis the unit cell contains Ca19.66 Mg0.17 Na0.14 K0.08 Sr0.03 Li0.08 approximately 4[Ca5(SiO4)2SO4] and isostructural with silicocarnotite, 4[Ca5(PO4)2SiO4]. Type material is preserved at the Government Chemical Laboratories, Perth, Western Australia.

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 phase equilibrium diagrams of CaMgSi2O6-CaTiAl2O6 with 10, 20, and 30 wt % Ca2MgSi2O7 in the join CaMgSi2O6-Ca2MgSi2O7-CaTiAl2O6 were determined. Six three-phase assemblages, six four-phase assemblages, and two five-phase assemblages (isobaric trivariant, divariant, and univariant) were confirmed. The univariant assemblages are diopsidess+forsterite+åkermanitess + perovskite + liquid and diopsidess+åkermanitess+perovskite+spinel + liquid. Because of the complex solid solutions of diopside and åkermanite the crystallization ceases before invariant assemblages are reached and the final phase assemblage in the diopside-rich region is diopsidess+åkermanitess+perovskite, in the diopside-poor region diopsidess+åkermanitess+perovskite + spinel. Two invariant points, diopsidess+forsterite+åkermanitess+perovskite+spinel+liquid and diopsidess+åkermanitess+anorthite+perovskite+spinel+liquid in the silica-poor region of the system CaO-MgO-Al2O3-TiO2-SiO2 are estimated. The diopside solid solution in this join is discussed with its bearing on the natural titanpyroxenes from alkalic rocks including melilite.

A re-examination of the mineral scolecite has shown that the previously published monoclinic (pseudo-orthorhombic) unit cell is face-centred and that the Hermann-Mauguin spacegroup symbol has been incorrectly assigned. The reduced monoclinic cell yields a 9·85 Å, b 18·98 Å, c 6·52 Å, β 110° 61; space group Aa. New indexed powder data are included.

The cell dimensions of powder samples of some Bushveld titanomagnetites and ilmenites were determined using a 114·6 mm AEG Guinier camera. The average cell dimension of the titanomagnetite is 8·400±0·005 Å and there is no definite relationship between the cell edge of the samples and their position in the layered sequence. The average cell parameters of coarse-grained ilmenite are a 5·085±0·005 Å and c 14·09±0·02 Å. Ilmenite that has replaced ulvöspinel has on average a value of some 0·003 Å greater than that of associated coarse ilmenite grains.

Chemical analyses indicate that titanomagnetite from pegmatoidal plugs and from the top of layered sequence was generally subject to late-stage magmatic alteration and hence lies in the Titanomagnetite II field. In the Bushveld Complex there is an increase in the TiO2 content of titanomagnetite from some 12 % at the base to 18 % at the top of the Upper Zone. However, Bushveld titanomagnetite tends to be poorer in TiO2 than similar samples from the Skaergaard intrusion.

A discrepancy between modal and normative hercynite in the Bushveld samples indicates that a considerable amount of hercynite is probably still in solid solution in the titanomagnetite.

Chemical analyses of Bushveld ilmenites reveal that they lie in the same tholeiitic field as those of the Skaergaard intrusion.

Specimens of chlorophaeite and palagonite obtained from eight countries were examined using a variety of techniques. Investigations showed the materials to be not simple substances but multiphase composites. The confusion that existed in the literature necessitated a revision of the nomenclature and construction of criteria for identifying the two materials. Their nomenclature has been expanded: chlorophaeite to include the following phases; phase I, green and isotropic; phase II, golden yellow and isotropic; phase III, darker than phase II and anisotropic; a fourth phase, named associated material (A), microcrystalline, pale green and sometimes pleochroic. Similarly for palagonite, a golden yellow glassy phase, essentially basaltic glass (no new name needed); phase X, a hydrated phase slightly darker in colour than the glassy phase, also isotropic; phase Y, dark brown to orange, microcrystalline, anisotropic, found adjacent to phase X; associated material (M) green, anisotropic, often chlorite or chloritic. Both of the above descriptions were based on neotypes, established during the work. X-ray diffraction data for the two materials are given together with microprobe analyses of some of the phases of the two materials.

Compositional changes in chromites are shown to be related to the degree of alteration of the grains to ‘ferritchromit’. The chromium content of late stage pyroxenites and tremolites may be related to the development of the ‘ferritchromit’. Analysed grains from the chrome ores are shown to have a different chemistry to the accessory chromites in the peridotites.

A precise and accurate X-ray diffraction method has been developed whereby the weight percentages of aragonite and low- and high-magnesium calcite are determined from the integrated peak areas of spiked and unspiked samples. The spike mixture was prepared from organisms extracted from the samples to be analysed. Use of a spiking method also avoided the preparation of working curves from artificial mixtures of carbonate minerals, which may not have the same diffraction behaviour as the unknowns. A test of the precision of the method indicates the following coefficients of variation: aragonite, 1·4 %; low-magnesium calcite, 1·5 %; high-magnesium calcite, 7·8 %. A test of the accuracy of the method indicates no significant bias in any of the carbonate results, except in samples where high-magnesium calcite values are below 10 %. Quartz may also be determined by this method (coefficient of variation 23·9 %; positive bias in values greater than 10 %).

A minor phase in iron-ore sinters has been synthesized and identified as a clinopyroxene with the approximate formula Ca1·0(Ca0·14Al0·60Si1·08)O6. This composition shows that it consists largely of the hypothetical Tschermak's molecule, M2+SiO6. The small size and sparse distribution of this phase in most iron-ore sinters has previously hindered analysis.

From thermodynamic considerations of the system anorthite-åkermanite it appears that the effective molecular weights of the ‘molecules’ in the melts of this system are 0·5 the molecular weights of anorthite as well as that of åkermanite.

The effective molecular weight value of 0·5 anorthite is in significant contrast to that of 1 anorthite obtained by Adams and Cohen (1966) from a similar analysis of the system anorthite-diopside (Bowen, 1915, and Osborn, 1942). The analysis by Adam and Cohen would lead to a non-ionic silicate melt structure in the system anorthite-diopside in contrast to the accepted electrolytic view of silicate melts. It is suspected that the reason for this apparent difference lies in the published liquidus morphology of the anorthite primary fields of the system anorthite-diopside. This same liquidus morphology is also responsible for the distortions in the isofracts and isotherms in the high-temperature area of the primary field of anorthite of the system anorthite-åkermanite-diopside (de Wys and Foster, 1958).

Homogeneous glasses for the use as standards in electron-probe microanalysis were prepared as an alternative to natural minerals, oxides, and pure minerals. Homogeneity was achieved by careful grinding, mixing, and fusion of powders of known composition. Fusion was carried out under vacuum using a molybdenum boat. This method avoided bubbles and contamination and made it possible to achieve temperatures high enough for final mixing to occur during the fusion process. Nine glass beads each containing six to seven oxides were subjected to careful micro-probe examination. A statistical analysis of the results showed that for each element there was no significant difference in composition between the spots measured. As the analysing spot was of diameter 0·8 µ, this showed that the glasses were homogenous on a sub-micron scale.

A metallographic investigation of macro- and microstructure, supported in some instances by microprobe examination, has been made on a number of nickel-rich iron meteorites from the British Museum Collection. Monahans, Wiley, Cowra, and Deep Springs are considered together as plessitic irons rather than ataxites, whilst Morradal shows an unusual and coarse plessitic structure that has been altered by pre-terrestrial shock and reheating. Cape of Good Hope, Hoba, Tlacotepec, and Chinga show chemical and structural similarities and are discussed together, as are Weaver Mountains, Klondike, and Warburton Range. Meteorites considered separately include Kokomo, Piñon, Shingle Springs, South Byron, San Cristobal, Lime Creek, and Santa Catharina. Particular attention is paid to the presence of sulphides and of phosphorus-containing phases and their influence on the formation of the macro- and microstructure of these meteorites. Patches of oriented sheen form a macroscopic feature of the Cape of Good Hope group of irons and this effect is considered in relation to details of the microstructure. Attention is drawn to the fact that in Cowra, Piñon, Weaver Mountains, South Byron, and Morradal the troilite appears to have been remelted and dispersed by a shock event that operated at a temperature sufficiently high to allow obvious shock damage to anneal out of the metal phases.