bluuebunny/crossref_metadata_2025_split huggingface dataset:
The crystal structure of hohmannite, Fe2(H2O)4[(SO4)2O].4H2O and its relationship to amarantite, Fe2(H2O)4[(SO4)2O].3H2O
Authors: Scordari F. 
Published: December 2006

Hohmannite is a hydrated sulphate of ferric iron with the formula Fe2(SO4)2(OH)2.7H2O (Palache, Berman, and Frondel, 1951).Figs. 1 and 2 illustrate the structure of hohmannite. The first shows a complex chain of Fe(O, H2O)6 octahedra and SO4 tetrahedra, which runs along the c axis; the second visualizes the water molecules and an hypothetical hydrogen-bonds system obtained on the basis of electrostatic and geometrical considerations.
The geochemistry of loveringite, a uranium-rare-earth-bearing accessory phase from the Jimberlana Intrusion of Western Australia
Authors: Campbell I. H. , Kelly P. R. 
Published: December 2006

SummaryThe distribution and geochemistry of loveringite, an accessory Ti, Fe±Cr oxide containing U and rare-earth elements (Ln) from the Jimberlana Intrusion, have been studied. Loveringite is most abundant in bronzite cumulates; it is found in trace amounts in early plagioclase-augite-hypersthene cumulates, but is not found in the olivine cumulates or in the late-stage differentiates. Loveringites from the bronzite cumulates have a high Cr content compared with those from the plagioclase-augite-hypersthene cumulates, suggesting that the mineral is stabilized by the presence of Cr in the intercumulus liquid. The Ln pattern shows a strong depletion trend from La to Eu, a sharp reversal between Eu and Tb and a second depletion pattern from Tb to Lu. This pattern suggests that the Ln are substituting into two sites, one much larger than the other.
Amphibolitic rocks from the Precambrian of Grand Canyon: mineral chemistry and phase petrology
Authors: Clark Malcolm D. 
Published: December 2006

SummaryThe amphibolites and mafic schists that occur in the Precambrian metamorphic rocks of the Grand Canyon are divided into five major groups: anthophyllite and cordierite-anthophyllite rocks, early amphibolites, Granite Park mafic complex, hornblende-beating dykes, and tremolite-bearing dykes. Many types of amphibole occur in these rocks. Microprobe analyses identify gedrite, anthophyllite, cummingtonite, and grunerite, as well as three groups of calcic amphiboles. These last range in composition from colourless tremo-litic or actinolitic amphiboles, through pale-green horn-blende, to strongly pleochroic green-brown hornblende, which contains a significant proportion of the tscherma-kite and pargasite endmembers. Phase relationships between the coexisting amphiboles and other minerals are presented for two regional metamorphic events. Assem-blages containing chlorite, garnet, and hornblende were formed during the first event; from the absence of staurolite, but the presence of almandine garnet and oligoclase-andesine, it is concluded that the metamorphic grade was between the upper greenschist and the lower amphibolite facies. The second period of metamorphism produced rocks of the staurolite and sillimanite zones, within which three main ‘subfacies’ can be distinguished on the basis of phase relationships in the mafic schists.
Major element chemistry of the geothermal sea-water at Reykjanes and Svartsengi, Iceland
Authors: Arnórsson Stefán 
Published: December 2006

SummaryHigh-temperature geothermal fields in Iceland represent localized anomalies of hot, altered rock in the uppermost part of the crust, which coincide with points of maximum tectonic/magmatic activity. These points correspond to the intersection of oblique fault swarms to the plate boundaries. Geothermal activity under mid-ocean ridges follows probably similar tectonic/magmatic anomalies.Due to high permeability sea-water invades the bed-rock of the Reykjanes Peninsula, Iceland, and is overlain by a variably thick lens of dilute ground water of meteoric origin. The variable degree of salinity of geothermal waters in the Reykjanes Peninsula has resulted from different degree of mixing of fresh ground water with the underlying sea-water-ground-water in the downflow zones around the geothermal fields. At Reykjanes the geothermal water represents heated sea-water without any freshwater mixing. The difference in the composition of sea-water or sea-water/fresh water mixtures and the geothermal waters is due to basalt/water interaction at elevated temperatures. The major-element chemistry of the geothermal water represents an equilibrium composition at the relevant aquifer temperatures. The activities of silica, calcium, sulphate, and carbonate are thus limited by the solubilities of quartz, anhydrite, and calcite. Fluoride activity is thought to be controlled by an ionic exchange reaction where it substitutes for hydroxyl groups in phyllosilicates. The ratios of individual cations and hydrogen ion are governed by ionic exchange equilibria with hydrothermal minerals, probably smectite and chlorite. The equilibrium pH for the Reykjanes and Svartsengi geothermal waters is 5·5 and 5·1 respectively. Sea-water will become somewhat acid upon heating to more than about 300 °C and equilibration with basalt, the acidity increasing with temperature.
Normal and anomalous tobermorites
Authors: Mitsuda T. , Taylor H. F. W. 
Published: December 2006

SummaryTobermorite minerals vary in some proper lies, notably in whether or not unidimensional lattice shrinkage occurs by about 300 °C to give a 9·3 form; specimens that do this are called normal, and ones that do not, anomalous. Data are compared for thirteen natural tobermorites and the extent to which normal or anomalous character is related to other properties is examined. The most definite correlations found are with chemical composition and morphology. The conditions of formation of normal and anomalous tobermorites are discussed in the light of synthetic evidence.
Sedimentary analcime at Murrurundi, New South Wales, Australia
Authors: Nashar Beryl 
Published: December 2006

SummarySedimentary analcime in a small basin in Cainozoic basalt at Murrurundi, New South Wales, has probably resulted from the reaction of Na-rich water on colloidal nontronite derived from volcanic ash. Based on cell dimension (13.713 Å) and Δ2θ(1·81) determined by Saha's (1959) method it is a Group C low-silica type of Coombs and Whetten (1967).
Platinum-iron alloy sample containers for melting experiments on iron-bearing rocks, minerals, and related systems
Authors: Ford C. E. 
Published: December 2006

SummaryA method of producing platinum-iron alloy sample containers has been developed that allows experiments to be carried out on iron- and volatile-bearing systems with minimal net exchange of iron between the sample and its container. Preliminary experiments carried out using these containers in the temperature range from 1100 °C to 1250 °C and at pressures up to 10 kb over periods of up to 75 hours produced an average iron loss of 10% to 16% (as FeO) compared with more than 50% FeO loss obtained using pure platinum containers. A more judicious choice of alloy composition would reduce this loss still further.
Pargasite from the Eastern Ghats, Andhra Pradesh, India
Authors: Rao A. T. 
Published: December 2006

SynopsesHornblendes are not common in the charnockites of Kondpalli, but occur as an important constituent in the pyroxene granulites and pyroxenites of Seshadripuram hill. Analyses and optical data for two pargasites are given.
Allanite from the Kondapalli charnockites, Krishna District, Andhra Pradesh, India
Authors: Rao A. T. 
Published: December 2006

SynopsesThe coarse-grained charnockites of Donabanda hill, Kondapalli, contain metamict allanite. An analysis is given, also optical data for the heated allanite, and the conditions of formation of the rocks are shortly discussed.
I. Whiteite, a new species, and a proposed nomenclature for the jahnsite-whiteite complex series. II. New data on xanthoxenite. III. Salmonsite discredited
Authors: Moore Paul Brian , Ito Jun 
Published: December 2006

SummaryWhiteite, Ca(Fe,Mn)2+Mg2Al2(OH)2(H2O)8[PO4]4,a14·90(4) Å,b6·98(2) Å,c10·13(2) Å,β113° 07(10)′, Z = 2, space groupP2/a,α1·580(5),β1·585(5),γ1·590(5), 2V 40–50°, specific gravity 2·58, is a new species from the Ilha de Taquaral, Minas Gerais, Brazil. It is the Al3+-analogue of jahnsite. The mineral occurs as up to 5 mm tan crystals flattened on {001}. Twinning by reflection on {001} leads to pseudoorthorhombic development. Rather pure material also occurs from Blow River, Yukon Territory, Canada.For the general formulaXM(1)M(2)2M(3)2(OH)2(H2O)8[PO4]4, it is proposed that forM(3), Al3+> Fe3+, the established members of the series are whiteite—(CaFe2+Mg) and whiteite—(Mn2+Fe2+Mg); and for Fe3+> Al3+, jahnsite—(CaMn2+Mg), jahnsite—(CaMn2+Fe2+), and possibly jahnsite—(Mn2+Mn2+Mn2+).Xanthoxenite of Laubmann and Steinmetz (1920) is probably stewartite (in part) on the basis of morphological, optical, physical, and paragenetic evidence. The xanthoxenite of Frondel (1949) is proposed as the species type. It is triclinic,PorP1,a6·70(4) Å,b8·85(4) Å,c6·54(3) Å,α92·1(2)°,β110·2(2)°,γ93·2(2)°, Z = 1 for composition.Salmonsite,c.from Pala, California, is shown to be an intimate mixture of hureaulite and jahnsite on the basis of calculated and observed powder patterns and on reinterpretation of the original chemical analysis published by Schaller (1912). It is a breakdown product resulting from oxidation of Fe2+in the original hureaulite (‘palaite’) along with further aquation followed by fine-grained recrystallization. The reaction proposed is:
The growth of calcium metasilicate polymorphs from supercooled melts and glasses
Authors: Weston R. M. , Rogers P. S. 
Published: December 2006

SummaryThe morphology of calcium metasilicate produced during the crystallization of glasses and melts of approximately metasilicate composition has been investigated. Both isothermal heat treatments and a dynamic crystal-pulling technique were employed. The crystallization took place by a dendritic or spherulitic mechanism, according to which of the crystal polymorphs is stable under the prevailing conditions. The morphology of the crystals is controlled by the ease with which the anionic groups present in the amorphous phase can be incorporated into the growing crystals. This is reflected in the values of the activation energies of crystal growth found for α-CaSiO3 (160 kJ mol−1) and for β-CaSiO3 (319 to 383 kJ mol−1). The Keith and Padden theory of spherulitic crystallization was verified for the growth of β-CaSiO3 over a range of supercoolings. Time-temperature-transformation diagrams have been constructed from the experimental data.
Black elbaite from Corrego do Urucum, Minas Gerais, Brazil
Authors: Prescott B. E. , Nassau K. 
Published: December 2006

SummaryBlack tourmaline from Corrego do Urucum, Brazil, is an elbaite coloured by iron and manganese with blue, green, and pink regions. Polarized spectra show the absorption bands expected in elbaite (Fe-caused blue and green, and pink, which is probably caused by Mn). The colour distribution in the transverse sections does not conform to the symmetry of tourmaline and changes along the length of the crystals. Two distinct growth stages are indicated, separated by a partial dissolution and followed by another dissolution.
Structural state and composition of alkali feldspars in granites of the St. George pluton, south-western New Brunswick
Authors: Cherry Michael E. , Trembath Lowell T. 
Published: December 2006

SummaryThe variation in the structural state of potassium feldspars from the St. George pluton, New Brunswick, Canada, is discussed. Monoclinic potassium feldspars occur near the eastern end of the pluton whereas the granites at the western end contain triclinic potassium feldspars. Although the bulk compositions of the host rocks are all very near the granite minimum melt composition there is a systematic increase in the degree of ordering for both the triclinic and monoclinic suites of feldspars with the more ordered variants tending to occur within rocks nearest the minimum melt composition. There is more abundant textural evidence for the presence of a late-stage fluid phase in the granites containing the monoclinic potassium feldspars. It is proposed that a slower post-crystallization cooling rate was also a factor in the nucleation of triclinic domains in the potassium feldspars at the western end of the pluton.
Sasaite, a new phosphate mineral from West Driefontein Cave, Transvaal, South Africa
Authors: Martini J. 
Published: December 2006

SummaryA new mineral, sasaite, occurs as white chalky nodules in the soil of a dolomitic cave and seems to be derived from the action of bat guano on clay minerals. Under the microscope it consists of an agglomeration of plates 10–20 µm on greatest dimension and with a rhombic shape. Its formula is (Al, Fe3+)14(PO411(OH)7SO4·83H2O and it is orthorhombic or quasi-orthorhombic. Preliminary crystallographic data based on an orthorhombic cell are a 21·50, b 30·04, c 92·06 Å, Z10, based on a calculated density of 1·747 (observed 1·75). The optical indices are α 1·465, β 1·473, γ 1·477 all ±0·001, and the principal vibration directions are parallel or quasi-parallel to the crystallographic axis.
Magnetic chromites from Kondapalli, Andhra Pradesh, India
Authors: Rao A. T. 
Published: December 2006

SynopsesThe Kondapalli region (16° 37′ N. 80° 32′ E.) in the Eastern Ghats, Andhra Pradesh, consists of high-grade granulite facies rocks: charnockites, hypersthene granites, and enderbites are plutonic intrusives into khondalites—garnetiferous sillimanite granites, garnetiferous granites, siltimanite-garnet quartzites, and quartzites. Pyroxene granulites of gabbroic and noritic compositions are distinct basic intrusive bodies, occurring as sills and dykes.Chromite orthopyroxene nodules are enclosed in serpentinite and carbonate rock, formed from altered peridotite; they are younger than the charnockites and pyroxene granulites and are confined to the cores of south-eastern-plunging overturned isoclinal anticlines. The chromites are massive in coarse-layered pyroxenites and granular in fine-layered rocks; those found at Gangineni are magnetic and are associated with bronzite (En77–85), those from the Binny and Loya mines are non-magnetic and associated with enstatite (En88–95).Chemical analyses and X-ray powder data are given for five specimens, including both types. The magnetic susceptibility appears to increase with increasing Fe3+. The unit-cell size is negatively correlated with Cr3+, A13+, and Mg2+and positively with Fe2+and Fe3+.
Textural evidence for liquid immiscibility in tholeiites
Authors: Philpotts Anthony R. 
Published: December 2006

SummaryThe residual liquids of many tholeiitic basalts and andesites, on cooling, split into iron-rich and silica-rich fractions, which may quench to brown glassy globules and clear glass respectively. More commonly, however, cooling is sufficiently slow for the iron-rich liquid to crystallize to globular single crystals of pyroxene. Depending on the cooling rate, these crystallized globules range in shape from spheres to elongated globules bounded by crystal faces. The fine grain size of the mesostasis of most tholeiites is partly due to these small crystallized globules. The silica-rich fraction, on the other hand, is more commonly quenched to a glass, and when preserved as globules in the crystallized iron-rich fraction, it may be bounded by negative crystal faces of the surrounding pyroxene. Globules of the iron-rich liquid commonly nucleate on the surface of the plagioclase crystals where they can become trapped, later crystallizing to spherical pyroxene grains that mostly contain a minor opaque phase. In contrast, iron-rich globules that form next to pyroxene grains commonly become attached to these crystals, giving them lobate boundaries. The immiscible silica-rich liquid becomes trapped between these lobes and, with sufficiently slow cooling, results in finger-like quartzo-feldspathic inclusions extending in from the margins of the pyroxene grains. These textures can provide evidence of immiscibility in a wide range of volcanic and hypabyssal rocks, even when no glass is present.
Discordant calc-silicate bodies from the St. Just aureole, Cornwall
Authors: Alderton D. H. M. , Jackson N. J. 
Published: December 2006

SummarySeveral discordant, garnet-bearing bodies are described from the St. Just part of the Land's End granite aureole, Cornwall. It is suggested that these formed by a combination of metasomatic replacement and dilation with concomitant precipitation. Other Ca-Fe aluminosilicates (containing large amounts of Zn, Sn, B, and Be) are also present in the bodies. The chemical, petrographic, and field evidence suggests that the introduced material was transported by hydrothermal fluids. These fluids could well be related to the intrusion of the granite and the earliest phases of ore mineralization. Chemical analyses of garnets, calcic amphiboles and one apatite, epidote, diopside, and axinite are given.
Topotactic replacement of augite by omphacite in a blueschist rock from north-west Turkey
Authors: Carpenter M. A. , Okay A. 
Published: December 2006

SummaryPartial replacement of original igneous augite crystals by omphacite during blueschist metamorphism of a dolerite from the Mihalliççik area of north-west Turkey has been studied by transmission electron microscopy. The replacement occurred topotactically, apparently by ion exchange with a fluid phase, which left the basic pyroxene structure unchanged. Cation ordering in the omphacite caused a symmetry change from C-face centred to primitive with the formation of fine-scale antiphase domains. Selected-area diffraction provides evidence for P2 and P2/c space groups for the ordered omphacite though the best ordered areas show a tendency towards P2/n (reflections violating the n-glide are very weak) and also contain fine, wavy, disordered precipitates approximately parallel to (too).It is suggested that the replacement temperature was below the cation-ordering temperature and that the omphacite grew in a metastable, disordered state. Subsequent ordering occurred under irreversible conditions via a series of intermediate structures. The ordering sequence may illustrate the relationship between different ordering schemes in other blueschist pyroxenes.
Aegirine of possible authigenic origin in Middle Devonian sediments in Caithness, Scotland
Authors: Fortey N. J. , Michie U. McL. 
Published: December 2006

SummaryAn occurrence of aegirine in Middle Devonian lacustrine beds in Caithness is described. The mineral occurs as euhedral to subhedral prismatic crystals within a finely laminated siltstone. Microprobe analyses reveal a remarkably ‘pure’ composition consisting almost entirely of Na, Fe3+, Si, and O. X-ray diffractometry yielded the unit cell data: a 9·657 Å, b 8·800 Å, c 5·296 Å, and β 107·37°. Comparison with other natural aegirine compositions shows marked differences from those of igneous or metamorphic origin but a close similarity to a unique occurrence of authigenic aegirine in the lacustrine Green River Formation of Wyoming, U.S.A. Consideration of the nature of the Caithness occurrence, and comparison of the Devonian Orcadian basin with the Eocene Green River basin indicate similar geological environments. It is suggested that the mineral formed in hypersaline conditions in which sodium may have been derived from contemporaneous alkaline volcanism within the Orcadian basin.
Study of the sector structure in adularia by means of optical microscopy, infra-red absorption, and electron microscopy
Authors: Akizuki Mizuhiko , Sunagawa Ichiro 
Published: December 2006

SummarySurface microtopography of habit faces, and internal textures of corresponding growth sectors of adularia from the Rhonegletscher, Switzerland, and the Seikoshi mine, Japan, were studied by means of optical polarizing microscopy, reflection interference contrast, electron microscopy, and infra-red absorption spectroscopy. Thin sections parallel to the growth plane were prepared from the specimen whose as-grown face was pasted on a glass slide. Most internal textures seen optically in the thin sections correlated well with the growth patterns for both specimens (fig. 1). Thin foils prepared by ion-thinning from the Rhonegletscher adularia show, under the electron microscope, coexisting heavily cross-hatched areas giving diffuse diffraction spots and homogeneous areas giving sharp diffraction spots. As a whole, adularia from the Seikoshi mine gives more homogeneous and much weaker cross-hatching than the Rhonegletscher specimens. Also, infra-red absorption spectra, which correlate very well with the Al/Si ordering and the optics, show that the {110} growth sector consists of triclinic disordered K-feldspar and the {001} and {01} sectors monoclinic high or low sanidine or orthoclase.These observations indicate that the characteristic internal textures seen on all optical micrographs are formed during the process of crystal growth, and are not due to monoclinic-triclinic transition. Although the transition process has taken place to a slight extent, the original growth textures remain well preserved throughout geological time. It is suggested from these observations that the degree of Al/Si ordering is mainly controlled by the different rates of growth and the different two-dimensional atomic arrangements exposed on the various growth surfaces. The higher the growth rate the more disordered are the phases that form. The symmetry of the two-dimensional atomic arrangement is kept during growth regardless of the degree of ordering; {001} and {01} growth sectors whose crystal surfaces are parallel to b-axis are monoclinic, and the {110} sector whose surface is inclined to the b-axis is triclinic.
Stratiform magnetite crystals of abnormal morphology from volcanic carbonatites in Tanzania, Kenya, Greenland, and India
Authors: Deans T. , Seager A. F. 
Published: December 2006

SummaryMagnetite is common in carbonatites, and usually has octahedral habit. Abnormal crystals from Galapo, Tanzania, were long thought to be unique, but such crystals are now known to occur at seven localities in four countries. The magnetite is titaniferous, but not unusual in composition for its provenance. The abnormal crystals typically have large growth pyramids extending in one direction (occasionally in two or more directions). They appear to be formed by superimposition of macroscopic growth sheets, parallel to octahedral and other planes, giving a planar structure to the growth pyramid. The edges of the sheets may form low-index or more complex surfaces. Some sheets project beyond the bounding planes of the growth pyramid, which is not repeated in crystallographically equivalent orientations. This unusual mode of growth will be called stratiform. Recognition of these distinctive crystals elsewhere might reveal the presence of hitherto unsuspected carbonatites.
Hydrous gem magnesian cordierite with inclusions of hydroxyapatite, dolomite, and rutile
Authors: Graziani Giorgio , Guidi Gioli 
Published: December 2006

SummaryAn uncommon sample of a pale-blue Madagascar cordierite and its mineral inclusions of different kinds have been studied. The physical properties of the embedding cordierite are: α = 1·528, β = 1·522, γ = 1·537, δ = 0·009, 2Vα = 96°, density = 2·534 g/cm3, a = 17·082 Å, b = 9·728, c = 9·352, Δ = 0·26. The electron probe analysis gave SiO2=48·64%, Al2O3 = 35·08, FeO = 0·70, MgO = 12·35, H2O+ = 2·50. This is therefore a hydrous magnesian cordierite. Its structural state is related to the shift in α, β, γ, 2Vα, and Δ with heating. Probe analyses were performed on the inclusions: hydro-xyapatite, dolomite, and rutile. The occurrence of dolomite suggests the conditions of formation of the host mineral.