bluuebunny/crossref_metadata_2025_split huggingface dataset:
An anorthite-epidote-garnet-hornfels from Namaqualand, South Africa
Authors: Coetzee C. B. 
Published: December 2006

The present communication deals with a calc-silicate hornfels of uncommon mineralogical and chemical composition. It may be tentatively referred to the deep-seated metamorphism of a marl, and on account of the shortage of analytical data pertaining to metamorphosed sediments of the calcareo-argillaceous type, a detailed investigation of a variety of this group seems justified.Intercalated bands of anorthite-epidote-garnet-hornfels bordered bilaterally by pyroxene-bearing gneisses occur on the farms Zandfontein, Pella, and Klein Pella in the north-eastern part of the division of Namaqualand, South Africa (cf. geological map), On Klein Pella small exposures also extend intermittingly for approximately 1·5 miles due WNW.-ESE. of the amphibolite koppie situated on the northern boundary of the farm area. The bands exhibit a gentle pinch and swell structure with maximum widths of 15 to 41 inches, and the contact with the host rock is commonly marked by an epidotic fringe ¾ inch in thickness. In some cases the anorthite-epidote-garnet-rock is penetrated by parallel lenticles of pure quartz which may attain maximum breadths of 0·8 inch.
Tricalcium disilicate (rankinite), a new mineral from Scawt Hill, Co. Antrim (With Plate V)
Authors: Tilley C. E. 
Published: December 2006

Tricalcium disilicate, first described by Shepherd, Rankin, and Wright in their investigations on the lime–silica and lime–alumina–silica systems has since been reported as a constituent of technical slags. An account has also been given of its occurrence as a reaction product in a glass furnace.In the ternary system CaO–Al2O3–SiO2 the compound forms with pseudowollastonite–gehlenite and larnite–gehlenite two three-phase equilibrium assemblages, associations which are in part recorded in the technical products.G. V. Wilson recorded the disilicate together with wollastonite and melilite in reconstituted limestone fragments enclosed in glass, while S. G. Gordon has described and presented an analysis of a slag composed of pseudowollastonite and the 3:2-compound approaching in composition that of the binary eutectic in the synthetic system.
Preliminary observations on the distribution of trace elements in the rocks of the Skaergaard intrusion, Greenland
Authors: Wager L. R. , Mitchell R. L. 
Published: December 2006

The Skaergaard intrusion of Kangerdlugssuak, East Greenland (68° 10′ N., 31° 40′ W.) contains a series of gabbros and related rocks—the layered series—which has been interpreted as the result of fractional crystallization of a fairly normal gabbro magma (Wager and Deer, 1939). Analysis of these rocks and of some of the constituent minerals by Dr. W. A. Deer has shown a considerable and systematic variation in the major constituents (1939, table XXXVI and pp. 67–84) and it was considered therefore that it would be of value to determine the variation in some of the rarer elements.The work of Goldschmidt and his collaborators on the distribution of trace elements in minerals (summarized in Goldschmidt, 1937) combined with our recently acquired knowledge of many crystal structures has made clearer the factors controlling the distribution of the trace constituents in minerals.
A method of tracing the temperature and oxygen-fugacity histories of complex magnetite-ilmenite grains
Authors: Bowles John F. W. 
Published: December 2006

SummaryThe formation of ilmenite from titanomagnetite frequently shows separate generations of production. The ilmenite products can be combined with the magnetite host to represent the intermediate stages in this development. Use of the Buddington and Lindsley (1964) geothermometer in conjunction with this method provides a number of points in the temperature and oxygen-fugacity history of a single, complex magnetiteilmenite grain.Application of the method is illustrated by an example from the Freetown layered gabbro. A titanomagnetite exsolved granular ilmenite whilst cooling and this process ceased at 930° and an oxygen fugacity of log ƒO2 = −11·5. Further cooling and exsolution continued until the grain reached 662 °C and log ƒO2 = −19·0, producing distinct ilmenite lamellae.
A metallographic and microprobe examination of a metallic nodule from the Bondoc Peninsula meteorite
Authors: Axon H. J. , Nasir M. J. 
Published: December 2006

The Bondoc Peninsula meteorite appears to be unstable and is disintegrating as the result of terrestrial corrosion. The meteorite is complex with occasional 1 to 3 cm dia. ‘Nodules’ of ‘iron-class’ material, fig. 1, within which are numerous non-metallic inclusions. These range in size from 0·5–1·5 mm and vary in shape from the extremes of angular to globular, shown in figs. 2 and 3. The metallic groundmass of fig. 1 is a polycrystalline array of kamacite grains that are equant in shape and about 3 to 4 mm dia. The boundaries between these kamacite grains are heavily invaded by corrosion product. The films of cracked schreibersite and strips of compositionally zoned taenite that are present at the kamacite boundaries each contribute about 2 % by volume and their average Ni contents are about 45 wt% and 40 wt% respectively. When these figures are combined with the average 6·2 wt% Ni, 0·75 wt% Co, and 0·02 wt% P of the kamacite the resulting bulk composition of the metal is ∼ 7·5 wt% Ni, ∼ 0·7 wt% Co, ∼ 0·3 wt% P. Nital etching reveals partially annealed Neumann bands in the kamacite, indicating a late stage reheating below about 500°C. However, the M profile method of Wood (1967) when applied to the zoned taenite yields a cooling rate of 0·1–0·5°C/Myr before this reheating event.The angular inclusions are relatively coarsely crystalline and commonly have massive chromite and tridymite crystals, with pyroxene, anorthite, and whitlockite usually present. Most angular inclusions also contain small particles of metal (10–40 µm dia.) interstitial to the mineral phases in the depth of the inclusion. Small quantities of sulphide and phosphide are similarly located. The metal in the angular inclusions is not detectably zoned and both kamacite and taenite show a range of Ni contents that vary with particle size in the manner previously observed by Powell (1969) for a range of conventional mesosiderites. We have in addition measured the Co and P contents of this metal and find P < 0·1 wt% and the Ni and Co analyses are consistent with equilibration in the ternary Fe-Ni-Co equilibrium diagram at ∼ 450 °C.
A hydrothermal deposit from the floor of the Gulf of Aden
Authors: Cann J. R. , Winter C. K. , Pritchard R. G. 
Published: December 2006

SummaryFragments of a hydrothermal deposit, partly moulded on pieces of basalt lava, were dredged from the edge of the median valley in the centre of the Gulf of Aden. The deposit consists of two main components, manganese oxide in the form of spongy brown to hard black lumps and coatings, and friable green massive smectite. There are smaller amounts of an iron-oxide component, and mixed manganese-oxide-smectite material. Contents of the less mobile trace elements in the smectite are too low for it to have formed by alteration of basalt glass, and it is interpreted as a direct precipitate from hydrothermal solution. None of the components is enriched in Cu or Zn, or contains appreciable amounts of sulphur. If there are sulphides in this deposit, they must lie beneath the parts sampled.
The occurrence of paragonite in chloritoid schists from Stonehaven, Scotland
Authors: Baltatzis E. , Wood B. J. 
Published: December 2006

SummaryParagonite has been found in two chloritoid-chlorite-mica schists from the Dalradian, north of Stonehaven. The principal bulk-chemical constraints on the occurrence of this mineral within the chloritoid zone appear to be the ratios of soda to potash and the Al2O3 contents of the rock. The composition of paragonite coexisting with muscovite indicates a crystallization temperature of 550 °C for rocks some way above the chloritoid isograd. Although this result is supported by other mineral equilibria, the muscovite compositions suggest a temperature of 690 °C which is too high because the mineral assemblage chloritoid-paragonite is unstable above about 600 °C By combining data on the breakdown of the chloritoid-paragonite assemblage with a mineral equilibrium for the assemblage garnet-plagioclase-muscovite-biotite, it has been deduced that rocks close to the staurolite isograd crystallized at about 7·5 kb and 600 °C.
Plagioclase-alkali-feldspar geothermometry revisited
Authors: Powell Marjorie , Powell Roger 
Published: December 2006

SummaryThe plagioclase-alkali-feldspar geothermometer formulated by Stormer (1975) does not take into account the effect of small amounts of calcium in the alkali feldspar. This geothermometer has been reformulated using ternary regular solution model equations, and it is shown that as the Ca content of the alkali feldspar increases the temperature calculated using the Stormer geothermometer will be increasingly too high.
The structure of chloroxiphite, Pb3CuO2(OH)2Cl2
Authors: Finney J. J. , Graeber E. J. , Rosenzweig A. , Hamilton R. D. 
Published: December 2006

SummaryChloroxiphite, Pb3CuO2(OH)2Cl2, is monoclinic, space groupP21/m, witha= 10·458,b= 5·750,c= 6·693 Å, β = 97·79°,Z= 2. The structure has been refined by the method of least squares from three-dimensional Mo-Kα intensity data to a conventionalRvalue of 0·115. The structure consists of sheets of composition [Pb3CuO2(OH)2]2−, in themselves made up of the layer sequence Pb-(O, OH, Cu)-Pb, lying parallel to (01). The structure contains eight-fold PbO4Cl4and seven-fold PbO5Cl2polyhedra common in other oxychlorides, Pb6clusters and copper atoms in square planar, Cu(OH)4, coordination.
Al-rich pyroxene and melilite in a blast-furnace slag and a comparison with the Allende meteorite
Authors: Butler B. C. M. 
Published: December 2006

SummaryFassaitic diopside containing 22–23 wt% Al2O3 (approximately 41–43% calcium Tschermak's molecule, CaAl2SiO6) and melilite containing 69–43% gehlenite crystallized from a blast-furnace slag at atmospheric pressure between about 1450°C and 1250°C. The occurrence is of petrological interest because the association of pyroxene with gehlenite-rich melilite has not been recorded from experimental studies in the system CaO-MgO-Al2O3-SiO2, and because of the similarity of the compositions of both minerals to pyroxene and melilite in the Ca-Al-rich inclusions of the Allende meteorite.
Conditions of phlogopite crystallization in ultrapotassic volcanic rocks
Authors: Edgar A. D. , Arima M. 
Published: December 2006

AbstractPhlogopite occurs as an early crystallizing mineral in many ultrapotassic lavas of basaltic affinities. Based on high-pressure experiments in lavas of these compositions, the early crystallization of phlogopite is controlled in large part by the bulk compositions of the liquids from which it crystallizes but also by the total pressure and by the aH2O, with early phlogopite forming under a narrow range of aH2O, less than that represented by H2O-saturated conditions. Variations in fO2 do not appreciably affect phlogopite crystallization but high aCO2 suppresses its crystallization. In ultrapotassic magmas, phlogopite will preferentially incorporate K2O, TiO2, MgO, and Al2O3 relative to the coexisting early silicate minerals, olivine and clinopyroxene, and thus, on fractionation of these minerals, phlogopite will be more effective in reducing these oxides in residual liquids. Phenocrysts and microphenocrysts of phlogopite in ultrapotassic lavas are directly related with respect to their K/Ti, K/Al, K/(K + Na), and Mg/(Mg + Fe) ratios. Textural relations suggest phlogopite may form by reaction relationships involving liquid with olivine, and/or clinopyroxene. Such relationships are supported by the experimental studies on ultrapotassic rock compositions.
Infrared spectroscopic analysis of the olivenite-adamite series, and of phosphate substitution in olivenite
Authors: Braithwaite R. S. W. 
Published: December 2006

AbstractInfrared spectroscopy affords a rapid and easy method of estimating the position of a mineral in the olivenite-adamite solid solution series, and of estimating the amount of phosphate substitution in olivenites. Toman's discovery of the monoclinic symmetry of olivenites with up to approximately 20 atom % Zn/(Cu + Zn) has raised a problem in nomenclature. It is suggested that the definition of ‘cuproadamite’ be extended to cover all orthorhombic members of the series containing appreciable Cu. Studies of deuterated materials have helped to solve some of the absorption band assignments for olivenite-adamite, libethenite and related minerals.
The crystal structure of cesanite, Ca1+xNa4−x(SO4)3(OH)x · (1 − x)H2O, a sulphate isotypic to apatite
Authors: Tazzoli V. 
Published: December 2006

AbstractCesanite, Ca1+xNa4−x(SO4)3(OH)x · (1 − x) H2O, is hexagonal, space group P63/m, a = 9.446(1) and c = 6.895(1) Å, Z = 2. The crystal structure refinement, carried out by utilizing 457 independent reflections (final R = 0.021), shows that cesanite is isotypic to hydroxyapatite. The P atom of apatite is completely replaced in cesanite by an S atom; the two independent Ca sites of apatite are occupied respectively by Na and Na + Ca, the charge balance being by partial substitution of H2O for OH− although the occupancy of the (H2O,OH−) sites is not complete. The relationship between the water vacancies and the structural features of the (Ca,Na) polyhedron is discussed. A new general formula for the apatite-wilkeite-ellestadite series is proposed.
Further data on the occurrence of pectolite in kimberlite
Authors: Scott Smith Barbara H. , Michael Skinner E. , Roger Clement C. 
Published: December 2006

AbstractPectolite has been identified, using petrographic, chemical, and X-ray methods, in kimberlites from the De Beers and Dutoitspan Mines, Kimberley, South Africa and the Letseng-La-Terai Mine, Lesotho. It occurs as radiating aggregates of fibrous or acicular crystals not only in the groundmass of certain kimberlites but also in altered xenoliths included within kimberlite. The occurrence of Na-rich minerals in kimberlite is unusual. It is suggested that it can occur as an apparently primary mineral resulting from the incorporation and assimilation of foreign Na-bearing material prior to final consolidation, and/or as a secondary mineral after metasomatic introduction of Na-bearing fluids.
Mafic silicates from the nepheline syenites of the Motzfeldt centre, South Greenland
Authors: Jones A. P. 
Published: December 2006

AbstractAt least five successive intrusions of nepheline-bearing magmas fractionated in situ and developed repeatedly overlapping, yet distinct chemical trends in the mafic silicates. Representative electron probe analyses are given for olivine, clinopyroxene, amphibole, biotite, and aenigmatite and their variations discussed. Increasing Na with fractionation produced aegirine-rich clinopyroxene and caused Na/K in amphibole to increase from 2.4 to 7.0. Siz/Alz increased in both amphibole and in the less abundant mica. Mn-enrichment is common to all of the mafic silicates, including the olivines and it is suggested that the parent magmas were initially Mn-rich.Mineralogically the Motzfeldt centre is evolved and similar to the other centres in the Igaliko complex. However, the Motzfeldt centre contains the most fractionated rocks (lujavrites) and is in this respect similar to the peralkaline Ilimaussaq intrusion. The compositional ranges and trends of the mafic silicates in Motzfeldt thus provide links between the uncommon peralkaline plutons and the more abundant and typical nepheline syenites.
Inclusion patterns in zoned garnets from Magerøy, north Norway
Authors: Andersen T. B. 
Published: December 2006

AbstractGarnet porphyroblasts in metasediments from Magerøy crystallized during static metamorphism. They display three optical zones, each having characteristic inclusions and chemistry. The compositional zoning is related to prograde metamorphism (an inner zone, 1, and a graphite-bearing zone) and retrogression (the outer zone, 2). Inclusions of two types are present in zone 1: type 1 are equidimensional remnants of the matrix, preferentially included along planes of rapid growth; type 2 are tubular and represent recrystallized quartz grains concentrated along defects in the garnet lattice. The defects are lineage boundaries between growth segments related to screw dislocations on crystal faces. Crystal growth developed at relatively high degrees of supersaturation, but below the supersaturation required for the development of dendrites. The inclusions suggest rapid growth of zone 1, caused by heat flow from an adjacent interkinematic mafic/ultramafic intrusive complex. The graphite-bearing zone crystallized at the metamorphic peak, while the inclusion-free idioblasfic rim probably developed during retrograde metamorphism.
Uvarovite and grossular from the Fengtien nephrite deposits, eastern Taiwan
Authors: Wan Hsien-Ming , Yeh Chun-Lu 
Published: December 2006

AbstractUvarovite and grossular, the former comparatively rare, occur along the serpentinite-graphite schist contact in the Fengtien area, on the eastern slope of the Central Range of Taiwan. Uvarovite occurs as small emerald-green euhedral crystals on diopside-fels with dodecahedral crystal forms and many other modifications. Its refractive index is 1.782, specific gravity 3.702, and unit cell edge 11.912 Å. Chemical and probe analyses give average Cr2O3 contents of 11.60 wt. %; spectrographic analysis shows significant enrichment in Cr, Be, Co, Y, Sb, and La over grossular. Associated minerals include nephrite, diopside, tremolite asbestos, zoisite, and clinozoisite. Grossular is reddish-brown; large crystals, dodecahedral in form often modified by trapezohedrons, are associated with diopside, idocrase, and calcite. n = 1.746, SG = 3.636, and a = 11.866 Å. Structurally and chemically it is quite near the grossular end member. Grossular is considered to be formed from pneumatolysis associated with the intrusion of ultramafic rocks, whereas uvarovite is a replacement product of relict chromite in the original ultramafic rocks where migration of elements such as silicon and calcium from wall rocks are prominent.
Crystallization trends of pyroxenes from agpaitic phonolites (Cantal, France)
Authors: Brousse R. , Rançon J. Ph. 
Published: December 2006

AbstractCa- and Na-rich pyroxene compositions of four agpaitic phonolites from the Cantal Volcano (France) have been studied. The pyroxenes from each sample show a range of compositions between X2+ pyroxencs (with X = Ca, Mg, Fe2+) and aegirine. The main substitution, X2+ by (Fe3+ + Na+), occurs when Na-Mg = 0.5, by which time Si is already equal to 2.0. The crystallization of Fe-Na-rich pyroxenes seems to be related to the increasing peralkalinity of the environment, in which the initially high temperature was suddenly reduced. Other factors, such as the structure of the liquid, are also considered.
The obliquity of K-feldspar from schists, gneisses, and granites in the north-eastern part of the Hida metamorphic belt, central Japan
Authors: Fujiyoshi Akira 
Published: December 2006

AbstractMost of 325 K-feldspars from the Hida metamorphic belt are characterized by diffuse 131 and 11 reflections. These K-feldspars are classified into eight obliquity types on the basis of the width of the 131 peak or the ratio of mean height of two outer peaks (131 and 11) to that of the middle composite peak. From the distribution of obliquity types and the microscopic characteristics of K-feldspars, this area is divisible into six zones.The feature of each zone is shown by the frequency distribution of eight obliquity types in each zone, which reflects the strength of later retrogressive effects. The frequency distribution of Δ values in each of the types IV-VIII provides further information on later events.The result of the K-feldspar study possibly indicates that the inversion of monoclinic to triclinic K-feldspar, characterized by the development of perthitic texture or crosshatched twinning, is sensitive to the degree of later retrogressive events. Some data on 2θ values of 04, 060 and 01 reflections in each types are presented.
The structural behaviour of tetrahedral framework compounds — a review Part II. Framework structures
Authors: Taylor D. 
Published: December 2006

AbstractTetrahedral framework compounds, as defined in this paper, generally exist as tilted and distorted versions of ideal fully expanded structures at room temperature and atmospheric pressure. How pressure, temperature, and composition (P, T, andX) affect the tilting and distortion is critically reviewed. It is shown that although the effects ofP, T, andXon the cell parameters are broadly analogous, the underlying structural changes are generally different. An important, and frequently neglected thermal effect is the apparent shortening of the framework bonds by the anisotropic thermal motion of the framework oxygens. Tilting models of framework compounds are critically examined and their failure to match the observed structural behaviour is attributed to changes in tetrahedral distortion. For quartz it appears that during compression the change in tetrahedral distortion is virtually all angular (O-Si-O angles), whereas during thermal expansion the change in distortion is in the Si-O distances. Such behaviour may typify the behaviour of many other framework compounds but the structural data needed to establish this are lacking. The review is illustrated by reference to the quartz and cristobalite analogues; to the sodalite, leucite, nepheline, scapolite, and feldspar families; and to the nitrides and oxynitrides of silicon and germanium. It is concluded that our understanding of the structural behaviour of framework compounds is still superficial and that much theoretical and experimental work remains to be done.
Eggletonite, the Na analogue of ganophyllite
Authors: Peacor Donald R. , Dunn Pete J. , Simmons William B. 
Published: December 2006

AbstractEggletonite is a new mineral, the Na analogue of ganophyllite. Type material has composition(Na0.82K0.40Ca0.39□0.39)Σ2.00 (Mn6.61Zn0.08Mg0.16Fe0.61Al0.56)Σ8.02 (Si10.33Al1.67)Σ12.00[(O28.92(OH)3.08]Σ32.00 (OH)4.00·10.66H2O.It occurs as prismatic crystals elongated along [100] in miarolitic cavities in nepheline syenite at the Big Rock Quarry, Little Rock, Arkansas. Single-crystal X-ray diffraction data are consistent with space group I2/a or Ia; a = 5.554, b = 13.72, c = 25.00Å, β = 93.95° Z = 2; this is equivalent to the substructure of ganophyllite. Physical properties include cleavage: {001} perfect; colour: dark brown; translucent; streak: light brown; hardness (Mohs): 3–4; brittle; observed density 2.76, calculated density 2.76 g/cm3. Optically, eggletonite is biaxial negative, with optical parameters 2Vα = 9(3)° r < ν, weak; indices of refraction α = 1.566(2), β = 1.606(2), γ = 1.606(2); pleochroism is very weak, γ ≃ β > α; α = pale brown to colourless, β ≃ γ = pale yellow brown. Principal lines in the X-ray powder diffraction pattern are (d, I/Io): 12.4, 100; 3.45, 15; 3.13, 30; 2.854, 15; 2.691, 25; 2.600, 20; 2.462, 20; 2.387, 15. The name is in honour of Dr Richard A. Eggleton, Australian National University.