Johnsomervilleite, Na10Ca6Mg18(Fe, Mn)25 (PO4)36 has Z = 3, a 15.00 Å, c 42.75 Å and cell volume 8330 Å3 and is a new rhombohedral species occurring in two metamorphic segregation pods in Moine gneiss of kyanite-sillimanite grade. Associated minerals are apatite, jahnsite, graftonite, mineral A, phosphosiderite, rockbridgeite, mitridatite, and vivianite. It is dark brown, brittle, and glassy, H = 4½, D = 3·35 (calc. 3.41) with a perfect basal (?) cleavage. Eight electron probe analyses are given and d spacings for 50 lines. The mineral, which is a Mg-Fe analogue of fillowite, is named after the late Mr J. M. Somerville who presented a specimen of garnet-quartz rock, which contained the new species, to the Royal Scottish Museum.

Glushinskite, a dihydrate of magnesium oxalate, occurs at the lichen/rock interface on serpentinite colonized by Lecanora atra at Mill of Johnston, near Insch in north-east Scotland. It is found in a creamy white layer intermingled with the hyphae of the lichen fungus. It consists of crystals mainly 2 to 5 µm in size showing a distorted pyramidal form, often with curved and striated faces. X-ray, infrared, and chemical data are given.

Gismondine is a monoclinic mineral but prior to X-ray determination of its unit cell it was variously regarded as orthorhombic, monoclinic, or triclinic on account of its intricate twinning. A study of gismondine crystals from Osa Quarry, near Rome, indicates that the morphologically dominant form is {32} which by twinning about the normal to {100} produces penetration-twinned octahedral crystals united on (100) and (001). Gismondine has poor cleavage on {32} optic plane is (010) and γ:[001] = 42.5° (in obtuse β).

A Miocene porphyry belonging to the sheshonite association contains 7 cm sanidine megacrysts in a groundmass of microphenocrysts of labradoritebytownite, augite, sporadic hastingsite, magnetite, sphene, K feldspar, apatite, Ca zeolite and calcite. The megacrysts (Or78–94) are enriched in BaO (≃ 2.0 wt%) and SrO relative to the groundmass. Although mineralogr and texture suggest that the megacrysts were suspended in a liquid, now represented by the groundmass, calculated liquid densities except for dry melts are less than those observed for the megacrysts and it is concluded that the original magma contained very little water. It possibly originated in a subduction zone with the main hycration taking place at shallow levels of intrusion during contact with groundwater. This produced zeolitization of the feldspars and may have played a part in the K enrichment at the margins of the sanidine megacrysts.

Unusual clinopyroxenes were synthesized in the study of the join CaFeAlSiO6-CaTiAl2O6 in air at I atm. Clinopyroxene solid solution, hibonite solid solution, X-phase, perovskite, and corundum are present, and at subsolidus temperatures the clinopyroxene singlephase field extends up to about 19 wt% CaTiAl2O6. The CaTiAl2O6 component in the clinopyroxene however increases beyond the clinopyroxene single-phase field and attains 23 wt%. These clinopyroxene solid solutions are extremely poor in SiO2 and extremely rich in Al2O3, Fe2O3, and TiO2, and more than half of tetrahedral sites are occupied by AlIV, contravening the aluminium avoidance principle.

Illite crystallinity determinations on Palaeozoic pelitic rocks, whose stratigraphic range runs from Lower Cambrian to Westphalian, indicate that anchimetamorphism has affected both the Lower and Upper Palaeozoic sequences. Two metamorphic episodes are in evidence, with the earlier, Caledonian, being of slightly higher grade. The higher anchizone crystallinity values are recorded from the Fishguard area in which mineral assemblages of the prehnite-pumpellyite facies have recently been recognized in basic igneous rocks. The later metamorphic episode has affected rocks to the south of the Variscan front. Here crystallinity values are low anchizone but some straddle the boundary with the diagenetic state. The Pembroke coalfield lies in this southern area and has coals largely of anthracite rank with volatile matter contents of between 10.1 and 5% Grade of metamorphism as indicated by crystallinity and by coal rank data from the Pembroke coalfield shows anomalous results to that described from the main South Wales coalfield. A neo-formed 2M illite from the Variscan spaced cleavage is described with analytical and X-ray diffraction data.

The chemical, mineralogical, and textural changes involved in the weathering of basalt have been traced through various stages from fresh rock (which has a cation exchange capacity of 10 meq/100 g due to the presence of a swelling chlorite mineral) to reddened basaltic rubble consisting of interstratified montmorillonite-illite, hematite, and anatase. The cation exchange capacities of the rocks increase progressively with the formation of secondary clay from labradorite as Al, Fe, and Ti accumulate and Si, Mg, Ca, and Na are depleted—much of the K is retained in the secondary clay mineral. The weathering is considered to be contemporaneous with the formation of the Antrim bauxites but not so intense.

The name hauchecornite has been applied in the literature to a group of minerals with similar crystal structures and the general formula (Ni,Co,Fe)9ABS8, where A and B are As, Sb, Bi, and Te in two nonequivalent structural sites. A classification of the group is proposed based on the relative abundance of the elements As, Sb, Bi, and Te in the two sites. Hauchecornite is redefined as Ni9BiSbS8, the end-member being closely approximated by the composition of the material from the type locality, and a new name, bismutohauchecornite, is proposed for the Ni9Bi2S8 end-member. The classification, redefinition, and the new name have been approved by the Commission on New Minerals and Mineral Names, IMA.

Arsenohauchecornite, Ni9BiAsS8, and tellurohauchecornite, Ni9BiTeS8 from the Sudbury area, Ontario, are now recognized as distinct mineral species in the Hauchecornite Group and not as varieties as described previously. Descriptions of these two minerals are given, summarized from Gait and Harris (1972).

The incorporation of impurities in tridymites taken from a used silica brick have been studied by means of a high-resolution microprobe, X-ray fluorescence, X-ray diffractometry, and optical microscopy. The bulk impurity content of the brick changes strongly from the hot zone (4.7 wt%) to the colder part of the brick (7.6 wt%), indicating material transport along the temperature gradient. The transport medium for migration processes is probably a melt occurring in narrow veins between large tridymite crystals at high temperatures. The average impurity contents of homogeneous tridymite single crystals are 0.49 wt% in the hot zone of the brick and 0.81 wt% in the cold zone. Al2O3, TiO2, and Na2O are main impurity constituents; the tridymites do not contain significant amounts of Fe2O3 or CaO. The a parameters of tridymites decrease by about 0.26% from 4.9837 Å to 4.9709 Å from the hot zone to the cold zone of the brick and the c dimension shows a smaller decrease (0.11 %) from 8.2023 Å to 8.1933 Å.

A new analysis of the type material of cheralite specifies the individual rare earth elements. Unit cell contents are: (REE1.58Th1.15Ca1.03Pb0.05U0.15)3.96 (P3.67Si0.33)4.01O16. Refinement of the cell parameters based on new XRD data shows that a = 6.7515 ± 0,0005 Å, b = 6.9625 ± 0.0005, c = 6.468 ± 0.0005, β = 103° 53′, giving a cell volume of 295.2 Å3. Space group P21/n.

The maghemitization process, by which magnetic minerals with spinel structure become progressively oxidized but remain single phase spinels, seems to be an important feature of submarine weathering. Whether the process takes place by the minerals acquiring oxygen from the sea-water or by the sea-water leaching out iron, the controlling process is the diffusion of Fe2+ in the spinel structure. Magnetic studies have suggested that during maghemitization the availability for oxidation of Fe2+ in the tetrahedral (A) sites of the spinel structure is much less than that in octahedral (B) sites. In this study the Fe2+-containing spinels FeAl2O4, FeCr2O4, FeGa2O4, and Fe2GeO4, in which Fe2+ is predominantly in either A or B sites were prepared, and the diffusion of Fe2+ was studied by (1) interdiffusion experiments with the Mg2+ counterparts and (2) oxidation experiments in air. Fe2GeO4 (Fe2+ in B sites) was found to be associated with a higher interdiffusion coefficient and lower activation energy than FeAl2O4 (75% Fe2+ in A sites). Oxidation/diffusion activation energies of 0.27 and 0.71 eV were assigned to Fe2+ in B and A sites respectively. The experiments thus provide support for the maghemitization model in which Fe2+ in B sites is preferentially oxidized.

The chemical stabilities of mendipite, Pb3O2Cl2, diaboleïte, Pb2CuCl2(OH)4, chloroxiphite, Pb3CuCl2O2(OH)2, and cumengéite, Pb19Cu24Cl42 (OH)44, have been determined in aqueous solution at 298.2 K. Values of standard Gibbs free energy of formation, ΔGf°, for the four minerals are −740, −1160, −1129, and −15163±20 kJ mol−1 respectively. These values have been used to construct the stability diagram shown in fig. I which illustrates their relationships to each other and to the minerals cotunnite, PbCl2, paralaurionite, PbOHCl, and litharge, PbO. This diagram shows that mendipite occupies a large stability field and should readily form from cold, aqueous, mineralizing solutions containing variable amounts of lead and chloride ions, and over a broad pH range. The formation of paralaurionite and of cotunnite requires a considerable increase in chloride ion concentration, although paralaurionite can crystallize under much less extreme conditions than cotunnite. The encroachment of the copper minerals on to the stability fields of those mineral phases containing lead(II) only is significant even at very low relative activities of cupric ion. Chloroxiphite has a large stability field, and at given concentrations of cupric ion, diaboleïte is stable at relatively high aCl−. Cumengéite will only form at high concentrations of chloride ion.

The morphologies of hydrothermally grown reedmergnerite crystals change systematically with time and rate of change of B, Si order. Three stages in this process are recognized: (1) Growth of well-faceted crystals. (2) Development of etching leading to the formation of irregular grains. (3) Modification of irregular grains to form rounded or ellipsoidal crystals. A solutionreprecipitation process is responsible for the morphological changes and the increase in degree of order of B and Si with time at constant temperature and pressure.

Spectral reflectance measurements on three uniaxial ore minerals, tellurium, chalcopyrite, and stibioluzonite, which are opaque at least in the visible part of the spectrum have revealed that the reflectance curve of the ordinary ray varies with crystallographic orientation of the polished section. The three minerals possess symmetries capable of exhibiting optical activity in transmitted light. A possible explanation, therefore, of the anomalous behaviour is that the optical constants, i.e. the refractive index and the absorption coefficient, and thus also the reflectance, of the ordinary ray may differ for sections cut normal to c where optical activity probably has its maximum effect and for sections cut parallel to c where there is probably little or no complication due to optical activity. There would therefore appear to be a need to extend the theory of reflection from absorbing media to include reflection from optically active absorbing minerals.

Camptonite sills of Permian age, intruded into Cambrosilurian sediments, are present in the northern part of the Oslo region, immediately to the north of Gran, Hadeland. They have been considered, along with associated dykes of camptonite and other minor intrusions of maenaite, to be related to the predominantly gabbroic rocks comprising the Oslo-essexite plugs (Brögger, 1894). Porphyritic varieties of camptonite are the most common, containing phenocrysts of concentrically zoned clinopyroxene and concentrically zoned brown amphibole; but, aphyric varieties with abundant brown amphibole also occur. A second amphibole (actinolite) forms thin, patchy, green overgrowths to some phenocryst or matrix brown amphiboles.

The pyroxenes range in composition from diopside to sahlite. They contain up to 0.7% Cr2O3 in the most Mg-rich zones and up to 0.6% Na2O in the most Fe-rich zones. TiO2 and Al2O3 are in the ranges 0.5–3.8% and 3.0–9.2% respectively. These compositions are similar to pyroxenes from other camptonites and alkali basaltic and alkali gabbroic rocks. ‘Normal’ zoned phenocrysts, in which an outer pinkish zone surrounds a colourless core in thin section, have more Fe, Ti, and Al, and less Mg and Si in the outer zone. In ‘reversed’ zoned crystals, the slightly pinkish core contains more Fe, Ti, and Al, and less Mg and Si. Oscillatory zoning, restricted to three concentric zones (pinkish-colourless-pinkish) show the same chemical changes with colour variation. In terms of end-member molecules, substitutions involving CaTiAl2O6, CaAl2SiO6 plus CaFeSi2O6 replacing CaMgSi2O6 are responsible for the zoning.

The majority of the zoned brown amphiboles are kaersutite following the criteria of Leake (1978). Those zones with Ti < 0.5 atoms per formula unit range from titanian pargasite and titanian ferroan pargasite to titanian ferro-pargasite. These compositions are similar to kaersutites crystallizing from other camptonites and as inclusions, or as megacrysts and phenocrysts in alkali basalts and derivative rocks. A simple concentric zoning with more Fe and less Mg in the outer zones occurs; but, an oscillatory zoning pattern, with an intermediate lighter brown zone (containing more Mg and less Fe) between two concentric darker zones, is more common. Other elements do not show consistent variations between zones, but Ti generally increases with increase in Aliv.

It is postulated that the earliest pyroxene zones crystallized from an alkali basalt magma at approximately 20 km depth. Crystallization of the remainder of the pyroxene phenocrysts and the kaersutite took place at high temperatures (> 940 °C) and at probably greater depths (7–15 km) than crystallization of nearby exposed gabbroic plugs (Oslo essexites). A mechanism of alternate crystallization of pyroxene and kaersutite in response to changes in PH2O, with some partial resorption of the non-crystallizing phase, is suggested to account for the observed petrographic features and oscillatory zoning in both minerals. The actinolite is a product of late-stage metasomatic activity.

A number of diorite complexes occur within the Channel Islands region, notably on Jersey, Alderney, and particularly Guernsey. Much of northern Guernsey is made up of the largest of these complexes (fig. S1), the Bordeaux diorite. In the north-western part of this diorite, around Chouet, a complicated association of plutonic rocks occurs. Although the field relationships in this area are sometimes difficult to interpret—this is often the case in diorite complexes—three separate groups of rocks may be distinguished within the association: a diorite group; a granodiorite group; and an inhomogeneous suite of rocks (fig. S2).

The widespread diorite group consists predominantly of an even-grained diorite, which is relatively homogeneous but which occasionally grades into an acicular diorite, the latter often containing pods and veins of appinite. The granodiorite group is the least common, occurring as bodies which are interpreted as intrusive sheets and bosses within the even-grained diorite, but occurring as angular blocks within the inhomogeneous suite of rocks. The granodiorite invariably contains rounded diorite xenoliths. The inhomogeneous suite consists of a variety of rocks from patchy, dark diorite, through quartz diorite to tonalite. Commonly, these rock types are intimately associated, often showing gradational contacts with each other and frequently with the more basic portions occurring as ‘xenolithic’ material within the more acidic portions. At contacts between the inhomogeneous suite and the even-grained diorite certain features (e.g. lobate margins and pipe-like structures) indicate that the diorite must have been close to its solidus temperature at the time of emplacement of the inhomogeneous suite. The field relationships between the three groups are interpreted as indicating that the diorite group was emplaced first, followed by the granodiorite group, with both of these clearly pre-dating the inhomogeneous suite.

Fifty-nine specimens, chosen to give a representative sample of each of the three rock groups, have been analysed for major, minor, and a selection of trace elements and thirteen of these specimens have been analysed for REE. The chemistry of the analysed rocks confirms the division into three groups, with each group showing distinctive characteristics. Furthermore, chemical plots (e.g. Al2O3, P2O5, Cr, and Ni v. SiO2) show discontinuities and areas of overlap between each group which cannot be explained within the constraints of a single genetic model relating the three groups to each other. This argument is particularly strong for the relationship between the diorite group, which spans the range 50 to 59% SiO2, and the inhomogeneous suite, spanning the range 53 to 68% SiO2. In the area of overlap (53 to 59% SiO2) the two groups are geochemically different. Therefore, for a variety of reasons, including emplacement order, the geochemical characteristics of the groups and the lithological inhomogeneity which is associated only with the chemically intermediate members of the association (the inhomogeneous suite), three quite different and genetically unrelated liquids are required to generate the three groups of rocks.

The even-grained diorite shows chemical variation (e.g. with increasing SiO2, decreasing Al2O3, MgO, CaO, Sc, V, Cr, and Ni, and increasing Na2O, La, Nd, and Y) consistent with amphibole + plagioclase fractionation up to 55% SiO2. At 55% SiO2 several elements show a change of slope (e.g. FeO + Fe2O3, TiO2, Rb, Ba, and Zr) indicating the introduction of biotite as a fractionating phase. Increasing total REE content with increasing SiO2 throughout the even-grained diorite supports the contention that amphibole is an important fractionating phase. The higher TiO2, P2O5, Sr, La, Ce, Nd, and Y contents and negligible Cr and Ni contents of the acicular diorite suggest an origin by delayed crystallization of volatile-enriched portions of the diorite group magma.

The granodiorite group shows little geochemical variation. Members of this group contain detectable amounts of Cr and Ni, unlike virtually all members of the inhomogeneous suite. For this reason, and because of the field relationships, the granodiorite is considered to be genetically unrelated to members of the inhomogeneous suite and a separate liquid is thus required for its genesis. This liquid may have been the fractionated derivative of some other magma (though if this is so the ‘parent’ is entirely unrepresented at the present erosion level) or it may represent a direct crustal melt. Diorite xenoliths within the granodiorite are chemically similar to the even-grained diorite.

Despite the lithological complexity of the inhomogeneous suite, its geochemical unity is clearly established in that, for instance, virtually none of the members of the suite (including even the most SiO2-poor) contain detectable Cr and Ni. Moreover, geochemical variation within the group is rational (with the possible exceptions of Sr, Zr, and Ba) and may be explained in terms of a crystal fractionation model. However, the fractionation must have acted on a liquid itself unrelated to either the diorite or granodiorite group magmas. An additional complication is that later derivative liquids intrude into and partly digest earlier-formed semi-solids of the suite to produce much of the observed inhomogeneity. The phases which have controlled fractionation within the suite include plagioclase (established petrographically as well as geochemically) and hornblende. The role of apatite is uncertain. The fractionation of hornblende is particularly useful in explaining the change in REE contents within the inhomogeneous suite. Total REE contents increase from the dark diorite to the quartz diorite, but decrease from the quartz diorite to the tonalite with concomitant relative HREE depletion. This is taken to be a reflection of the changing hornblende/liquid partition coefficients for REE with increasing SiO2, which are less than one for liquids of basaltic and andesitic composition but greater than one for liquids of dacitic composition.

Hydrobasaluminite and basaluminite, two hydrated basic aluminium sulphate minerals have been found in the weathering zone of the Oxford Clay at Crook Hill Brickyard, Chickerell, near Weymouth, Dorset. Hydrobasaluminite occurs as a reaction rim surrounding carbonate concretions, and is believed to have resulted from the neutralization of aluminium-bearing acid sulphate solutions formed by oxidation of pyrite and subsequent leaching of clay. Basaluminite is found only on concretions that have fallen to the floor of the pit, suggesting that it is formed as a dehydration product of hydrobasaluminite.

Chemical analysis of hydrobasaluminite yields the composition 2Al2O3 · SO3 · 20H2O, although this almost certainly includes substantial amounts of adsorbed water. Chemical analysis of basaluminite gives the composition 2Al2O3 · SO3 · 9H2O, which is equivalent to a formula of Al4SO4(OH)10 · 4H2O if it assumed that water is present only as water molecules or hydroxyl ions. The sulphate ions are readily exchangeable. Electron-optical and X-ray powder diffraction data show the minerals to be monoclinic rather than hexagonal as previously reported. Indexed X-ray powder patterns give unit-cell parameters of a = 14.911(5) Å, b = 9.993(2) Å, c = 13.640(5) Å, β = 112.40(4)° for hydrobasaluminite and a = 14.857(3) Å, b = 10.011(3) Å, c = 11.086(7) Å, β = 122.28(3)° for basaluminite. The specific gravity of basaluminite is found to be 2.10 and Z = 4.

Hydrobasaluminite dehydrates irreversibly to basaluminite under normal laboratory conditions, but can be preserved indefinitely at high relative humidity. A study of the dehydration of basaluminite using a diffractometer heating-stage shows the presence of three further distinct hydration states as well as interstratified intermediates. The dehydrations occur topotactically and involve major changes in the c* direction only. DTA and TGA curves can be interpreted in terms of progressive dehydration.

It is suggested that the minerals possess a layer structure, probably containing gibbsite-like double-hydroxide layers with interlayer sulphate ions and water molecules. The data also seem to show a close structural relationship between basaluminite and the hydrated basic aluminium carbonate mineral, scarbroite.