bluuebunny/crossref_metadata_2025_split huggingface dataset:
Garnetiferous striped amphibolites from
Connemara, Western Ireland
Authors: Leake Bernard E. 
Published: December 2006

Summary
The chemical factors controlling the rare
appearance of garnet in Connemara amphibolites are
elucidated, including the importance of low
oxidation ratio (w), low Mg/(Mg+Fe+Mn) (mg), and
high MnO. Pressure is believed to be critical in
determining whether garnet is common in
amphibolites in any one terrain and it is
suggested that the ratio mg × w/MnO (called g) in
serial analyses of garnetiferous amphibolites can
be used as a measure of the pressure of
metamorphism.
89 Connemara amphibolite analyses with
plagioclase and hornblende are considered
including 31 new analyses, which are reported. Of
the 89 analyses, 10 contain garnet, 6
cummingtonite, 16 clinopyroxene including 3 with
garnet and clinopyroxene and 2 with garnet and
cummingtonite. The coexisting garnet and
hornblende in 3 amphibolites have been analysed,
including one sample in which brown-green and
green hornblende, cummingtonite, plagioclase,
garnet, and ilmenite have been analysed.
Cummingtonite does not coexist with clinopyroxene
or sphene and its presence is controlled by
pancity of Ca as well as medium to low pressure in
metamorphism.
Plagioclase-Ca-rich-nepheline intergrowths
in a syenite from the Marangudzi complex,
Rhodesia
Authors: Henderson C. M. B. , Gibb F. G. F. 
Published: December 2006

Summary
Nepheline in a basic syenite from the
Marangudzi complex is relatively Ca-rich with CaO
from 1·9 to 2·4 (wt) %. This Ca-rich nepheline
sometimes occurs in intimate intergrowths with
plagioclase (andesine). These intergrowths are
thought to have formed at temperatures in the
order of 750°–850°C by resorption of plagioclase
with simultaneous replacement by
nepheline.
Trace element geochemistry of parts of the Closepet granite, Mysore State, India
Authors: Rao V. Divakara , Aswathanarayana U. , Qureshy M. N. 
Published: December 2006

SummaryTrace elements in twenty samples of the Closepet granite (grey and pink varieties) and the related rocks have been determined by neutron activation analysis (Th, Rb, and Cs), fluorometry (U), flame-photometry (K), and emission spectroscopy (Pb, Sr). The trace element contents of the grey and pink varieties are generally similar. An analysis of the magnitudes of the trace element and other ratios (K/Rb, 235; Th/U, 6·4; U/K (× 104), 0·7; K/Cs (× 10−4), 3·6; Th/K (× 104), 5·3; Fe2O3/(FeO+Fe2O3), 0·27) as well as87Sr/86Sr initial ratio (0·705; Crawford, 1969) of the Closepet granite indicate two possible modes of genesis: Either the granite magma was not highly differentiated and the vapour phase was relatively insignificant; the crystallization of the magma took place under essentially non-oxidizing conditions; the pink variety, which followed the grey variety, crystallized under essentially the same conditions as the grey variety. Or the Closepet granite had a two-stage history—palingenesis (starting from the Peninsular gneiss) and metasomatism involving the enrichment in K, Rb, Pb, and Th and depletion of Sr and Cs, among others.
An interpretation of the hydroxyl contents
of biotites and muscovites
Authors: Forbes Warren C. 
Published: December 2006

Summary
The net cationic charge of the octahedral
and tetrahedral layers was calculated from the
analyses of 100 biotites and 93 muscovites and
compared to the observed hydroxyl contents
(OH+F+Cl). The correlation coefficient between
these parameters of −0·96 for biotites and −0·82
for muscovites demonstrates that the hydroxyl
content in these micas varies in response to
cationic substitutions. Thus substitutions in
micas involve cation-hydroxyl replacement couples
in addition to other modes previously recognized.
Tetrasilicic phlogopite,
K2Mg6Si8O22(OH)2,
which is related to phlogopite by the substitution
Al3+ +
H+ =
Si4+ was synthesized but is
not a stable phase under the conditions
investigated. This mica crystallizes as a 1M
polymorph with a =
5·289(2) Å, b =
9·151(3) Å, c =
10·247(3) Å, β =
100°4(2).
Exchange reactions, such as
Al3+ +
H+ ⇌
Si4+, between phlogopite and
pyroxenes at depth may provide a mechanism for
release of H+ within the
mantle.
A chromian tourmaline from Swat, West
Pakistan
Authors: Jan M. Qasim , Kempe D. R. C. , Symes R. F. 
Published: December 2006

Summary
Traces of a green chromian tourmaline
occur in calcareous rocks in contact with
serpentinite near Alpurai, Swat, West Pakistan.
The petrography of the rocks and the optical
properties of the tourmaline are presented along
with its chemistry (it contains over 8 %
Cr2O3
and about 0·2 %
V2O3).
The mineral is compared with other chromian
tourmalines and its paragenesis discussed: it is
thought to have been produced by silica-rich
hydrothermal (or gaseous) solutions, which have
crystallized as thin quartz veins in the
calcareous rocks, introducing boron and other
constituents.
Embreyite, a new mineral from Berezov, Siberia
Authors: Williams S. A. 
Published: December 2006

SummaryEmbreyite is a new mineral that has been found only in old specimens collected at Berezov, Siberia. The composition is Pb4·97(CrO4)2·00(PO4)1·91.0·75H2O, or Pb5(CrO4)2(PO4)2. H2O based on both wet and electron-probe analyses. Z = I, Dmeas 6·45, Deale 6·41. Crystals are monoclinic with a 9·755 Å, b 5·636, c 7·135, β 103°5′ the space group may be P21/m. No single crystals were found. α = 2·20, β = γ = 2·36. Colour in various shades of orange with a yellow streak. H = 3½; no cleavages observed. Occurs with vauquelinite, crocoite, and phoenicochroite in the oxide zone assemblage from Berezov.
Metasomatized (fenitized) quartzites from the Borralan Complex, Scotland
Authors: Woolley A. R. , Symes R. F. , Elliott C. J. 
Published: December 2006

SummaryFenitized quartzites are described from three localities around the Borralan alkaline igneous complex. Chemical and electron-probe analyses of amphiboles, pyroxenes, micas, and feldspars are given. Early-formed amphiboles are calcic, but these are replaced by alkaline varieties with increasing fenitization. Rock analyses indicate a ‘straight line’ rate of increase of Ti, Fe2+ + Fe3+, Mg, Al, K, and a more variable increase of Ca and Na atoms, at the expense of Si atoms. The simple composition of the unaltered quartzite allows the accurate calculation of bulk changes during fenitization. The final product of the alkali metasomatism is a syenite lying close to the albite-orthoclase minimum though the primary source of the fenitizing fluids was probably a highly potassic magma.
Talc-kyanite-quartz schists and other high-pressure assemblages from Zambia
Authors: Vrána S. , Barr M. W. C. 
Published: December 2006

SummaryTalc-kyanite-quartz schists, Mg-chlorite-kyanite-quartz schists, kyanite gedritites, and kyanite-bronzite gedritites occur in the Central Province of Zambia. Experimental work in the system MgO-Al2O3-SiO2-H2O suggests that these assemblages formed at pressures in excess of 10 kb.
New data on the composition of Caledonian granites
Authors: Hall A. 
Published: December 2006

SummaryNew analyses are given of granites from 23 intrusions in Scotland, Ireland, and the Isle of Man. Together with existing analyses, these were used to measure the regional variation in composition of Caledonian granites by means of trend surface analysis. An explanation of the variation is presented that involves the production of magma by melting in the crust, at a depth determined by the geothermal gradient.
X-Ray data and chemical analyses of some titanomagnetite and ilmenite samples from the Bushveld Complex, South Africa
Authors: Molyneux T. C. 
Published: December 2006

SummaryThe 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.
The decomposition and analysis of chrome spinel. A survey of some published techniques
Authors: Rodgers K. A. 
Published: December 2006

SummaryExamination of published procedures for the decomposition and subsequent analysis of chromite and chrome ores shows some to be unnecessarily complicated and time consuming. Others fail to yield consistent and reproducible results. Decomposition is rapidly and effectively accomplished using the peroxide frit technique of Rafter. Chromium may then be removed and determined volumetrically allowing the rest of the analysis to proceed along conventional silicate lines. Fe2+ is determined by oxidimetry following digestion with a mixture of phosphoric and sulphuric acids in the presence of ceric sulphate.
Calculation of crystal field splittings in
distorted coordination polyhedra: spectra and
thermodynamic properties of minerals
Authors: Wood Bernard J. , Strens R. G. J. 
Published: December 2006

Summary
A simple method has been developed for
calculating the
d-orbital energy levels
of transition-metal ions in coordination polyhedra
with both orthogonal and non-orthogonal
distortions, using equations based on those
derived by Ballhausen (1954). The input data are
atomic coordinates, a standard value of the
crystal field splitting parameter Δ at known
metal-ligand distance, and the ratio of radial
integrals
B2/B4,
which is approximately constant for a given ion.
The method can be applied to polyhedra containing
different ligands.
Application of the equations to the
Mn3+
(M3) site in piemontite
and the Fe2+
(M2) site in
orthopyroxene gives calculated transition energies
in good agreement with the observed band
energies.
The calculations permit definite
assignment of the great majority of
d-d absorption bands
even in multi-site phases, and enable
discrimination of crystal-field and
charge-transfer bands in mineral spectra. They
also throw light on the fine structures of both
oxygen → metal and metal → metal charge-transfer
bands, and allow the calculation of crystal-field
stabilization enthalpy and electronic entropy. The
latter is a previously neglected energy term that
contributes significantly to the energetics of
reactions within and between phases containing
transition-metal ions.
Melilite crystallization in the system
CaO-MgO-Al2O3-SiO2
Authors: Biggar G. M. , O'Hara M. J. 
Published: December 2006

Summary
The solidus temperatures (IPTS-68) and
melilite compositions (mole %) determined for some
four-phase assemblages in the system
CaO-MgO-Al2O3-SiO2
are: anorthite, diopside, spinel melilite
(Åk81Geh19),
1236·5 °C; diopside, spinel, forsterite, melilite
(Åk83Geh17),
1238 °C; foresterite, spinel, monticellite,
melilite
(Åk82Geh18),
1351 °C; monticellite, merwinite, spinel, melilite
(Åk52Geh48),
1378 °C; dicalcium-silicate,
Ca5MgSi3O12,
spinel, melilite
(Åk5Geh95),
ca. 1412 °C; dicalcium-silicate,
Ca6MgAl8SiO21,
spinel, melilite
(Åk4Geh96),
ca. 1347 °C.
Computer simulation of cation distribution
in the octahedral layers of micas
Authors: Krzanowski W. J. , Newman A. C. D. 
Published: December 2006

Summary
Without direct evidence that cations
favour particular sites in the octahedral layers
of phlogopite-biotite micas, it is usually assumed
that the cations are distributed randomly. Such a
distribution, however, implies appreciable
populations of cation combinations that seem
electrostatically improbable. A computer program
was written that rearranges a random distribution
so that the improbable combinations of cations are
eliminated by predetermined restrictions. Its use
shows that conditions deduced from Pauling's
electrostatic valence rule lead to grouping of
trivalent cations around vacancies; for some
chemical compositions, chains of alternate
trivalent cations and vacancies extend through the
structure.
Some chemical data on members of the
shoshonite association
Authors: Joplin Germaine A. , Kiss E. , Ware N. G. , Widdowson Jennifer R. 
Published: December 2006

Summary
A number of minerals and residual glasses
from absarokites, shoshonites, and latites have
been analysed by electron probe.
Clinopyroxenes show very little
iron-enrichment and these rocks are thus
distinguished from tholeiites and alkali
basalts.
Glasses from this group are also distinct
from tholeiites and alkali basalts and occupy a
separate field on a
CaO-Na2O-K2O
diagram.
Spinels from the Dawros Peridotite,
Connemara, Ireland
Authors: Rothstein A. T. V. 
Published: December 2006

Summary
Two different spinels, analyses of which
are given, occur in the layered ultramafic rocks
at Dawros. Chrome spinel occurs both as
gravity-stratified cumulates and as complex orbs,
while an Al-rich spinel is both in rocks of the
main Dawros magmatic sequence and in an
association with an aluminous bronzite, which may
originate by recrystallization. It is concluded
that while the chrome spinel is certainly of
magmatic origin, the aluminous spinel is probably
partly of magmatic and partly of recrystallization
origin.
Aguilarite from the Camoola Reef, Maratoto
Valley, New Zealand
Authors: Main J. V. , Rodgers K. A. , Kobe H. W. , Woods C. P. 
Published: December 2006

Summary
Aguilarite, Ag4SeS,
occurs in a hydrothermal vein deposit associated
with sphalerite, chalcopyrite, galena, and native
silver. Physical and chemical data agree with
descriptions from Guanajuato (type locality).
Differential thermal analysis of synthetic
material indicates an inversion temperature of
122±1 °C. The mineral crystallized late in the
paragenetic sequence, probably slightly above 200
°C.
Stressed pyroxenite nodules from the Jagersfontein kimberlite
Authors: Borley G. D. , Suddaby P. 
Published: December 2006

SummaryExamination of some pyroxenite nodules from the Jagersfontein kimberlite shows that they have suffered variable deformation followed by different degrees of recovery. Most interes~ting of the nodules is the 'diallage rock', which consists of highly sheared and broken lamellar crystals of diopside containing exsolved enstatite. Petrographic evidence indicates a pre-tectonic exsolution of enstatite and a syntectonic exsolution of pyrope-almandine from enstatite. Deformation occurred in the mantle, prior to incorporation of the nodule in the kimberlite. Compositions of pyroxenes from the diallage rock suggest it re-equilibrated at a temperature of 1000° and at a pressure of about 35 kb. Olivine and phlogopite, accompanied by serpentine, occur only in broken kink-bands in the diallage rock and they are considered to be of secondary origin, precipitated from kimberlite magma at temperatures near 700°
Lower Tertiary Tholeiitic Basalts from Southern New Caledonia
Authors: Rodgers K. A. 
Published: December 2006

SummaryEocene tholeiitic basalts occur throughout the length of New Caledonia where their emplacement preceded that of the peridotite massifs. In the south, two areas of basaltic rocks are intimately associated with Eocene sediments, which have been overridden by the peridotites. The aphyric, holocrystalline basalts consist of plagioclase, clinopyroxene, titanomagnetite, and minor quartz together with their abundant alteration products, which include epidote and uralite. The chemical compositions of these rocks fail to show agreement with oceanic tholeiitites, as suggested by earlier writers, although strong similarities exist with the basalts of the Papuan Ultramafic Belt.
Identification of iron-containing impurities in natural kaolinites using the Mössbauer effect
Authors: Hogg C. S. , Malden P. J. , Meads R. E. 
Published: December 2006

SummaryTwo clay samples originating in the kaolinized granite area near St. Austell, Cornwall, have been examined by Mössbauer spectroscopy. The iron-containing impurity in the sample with a red discoloration (sample A) has, by measurement of the hyperfine magnetic field, been identified as hematite. In the case of sample B, which was yellow in colour, preliminary Mössbauer work indicated β-FeOOH as the impurity, but detailed measurements of hyperfine field and Nöel temperature, when compared with similar results for a synthetic β-FeOOH sample, suggested otherwise. X-ray and chemical work suggested that the iron-containing phase in sample B is goethite, α-FeOOH in which some substitution of Al+3 for Fe3+ has occurred; the Mössbauer data are consistent with this conclusion. Both clay samples exhibited superparamagnetic behaviour and this has been utilized to obtain rough estimates of the mean radius of the particles of the iron-containing impurity. These were 117 Å for the α-Fe2O3 in sample A and 270 Å for aluminian α-FeOOH in sample B.
Carlfriesite, H4Ca(TeO3)3, a new mineral from Moctezuma, Sonora, Mexico
Authors: Williams Sidney A. , Gaines Richard V. 
Published: December 2006

SummaryCarlfriesite is a new species found in relative abundance at the Bambollita (now La Oriental) mine in the Sierra La Huerta near Moctezuma, Sonora. Colour primrose yellow (R.H.S. 4B) with pale yellow streak. H = 3½, Dmeas = 6·3, Dcalc = 5·93. Fair cleavage on {010}. Monoclinic with a 12·585 Å, b 5·658, c 9·985, β 115° 35′. Space group Cc or C2/c. Strongest lines are 3·167 (10), 3·082 (9B), 5·063 (6), 2.832 (6), 3·369 (4), 4·825 (3), 2·698 (3), and 4·o89 (2). Feeble pleochlroism in pale yellow with γ > α = β α = 1·982, β = 2·095, γ 2·19 2Vα, = 79° calc. Occurs with cerussite and chlorargyrite in an oxidized assemblage derived from hessite, galena, and bornite.
The crystal structure of schairerite and its relationship to sulphohalite
Authors: Fanfani L. , Nunzi A. , Zanazzi P. F. , Zanzari A. R. , Sabelli C. 
Published: December 2006

SummaryThe crystal structure of schairerite from Searles Lake, California, has been determined employing X-ray diffraction data collected on a single-crystal diffractometer. The crystal structure was refined by least-squares methods employing isotropic thermal parameters to a final R index of 0·07 for 2536 independent observed reflections. The cell content is 3[Na21(SO4)7F6Cl]. The space group is P31m with a 12·197 A and c 19·259 Å. Schairerite exhibits a marked sub-cell (a 7·042 Å, the same c axis and P3m1 symmetry), which may be related to the unit cell of sulphohalite when described in a hexagonal lattice.The crystal structure of schairerite may be considered as consisting of seven sheets of Na+ ions perpendicular to the c axis. These sheets are connected to each other .building up a three-dimensional framework. The Na+ ions in these sheets are arranged in an array built up of hexagons and triangles. Sulphur atoms lie in the sheets at the centres of each hexagon, the halogen atoms lying between the sheets midway between the centres of two triangles. A comparison with sulphohalite shows that the close lattice analogies may be related to a similar atomic arrangement. Apart from the differences in chemical formula (F:C1 ratio 1:1 in sulphohalite), the main difference in the structural framework consists of the unequal number of Na+ sheets (six in sulphohalite) and in the SO42− tetrahedra orientation.
Nickel-containing montmorillonites and chlorites from Brazil, with remarks on schuchardtite
Authors: Brindley G. W. , De Souza Jefferson V. 
Published: December 2006

SummaryClay-like, hydrous nickel silicates from Niquelandia, Goias, Brazil, and from Jacupiranga, São Paulo, Brazil, arc examined by X-ray diffraction, chemical analysis, and thermogravimetric methods. The nickel silicates from Niquelandia are ferric iron montmorillonites, with nickel in the octahedral positions and, to a lesser extent, in interlayer positions. The chemical compositions of samples dried at 110°C average (Mg0.15Ni0.08Ca0.015Na0.005) (Fe0.92IIIFe0.025IIAl0.55Mg0.37Ni0.22) (Si3.88Al0.12)O10(OH)2(H2O)0.93. The layer charge originates largely in the octahedral sheet. The cation-exchange capacities average 107 me/100 g clay (110°C). These minerals differ from non-tronites, in which the layer charge originates mainly in the tetrahedral sheets.The nickel silicates from Jacupiranga resemble chlorites, with a non-expanding basal spacing of 14·2-14·3 Å. The better crystalline forms give X-ray data in good agreement with a la polytype structure, which is consistent with their formation by low-temperature processes. Chemical formulae derived on the basis of O10(OH)8 give an average of 5·47 cations in octahedral positions. Thermogravimetric measurements show up to 4% H2O lost between 110 and 500 °C. These results suggest a partial vermiculitization of the interlayer sheets. A new method of calculating a structural formula is developed that gives an interlayer composition of the form R1.75(OH)3.75(H2O)1.14, with (OH + H2O)/R = 2·80, which approaches the ratio for a dioctahedral sheet structure.A comparison of these defect chlorites with available data on schuchardtites shows many similarities; however, schuchardtite is not yet sufficiently well denned for the Jacupiranga chlorites to be given this name.
Chemical variation among French ultramafic xenoliths—evidence for a heterogeneous upper mantle
Authors: Hutchison R. , Chambers A. L. , Paul D. K. , Harris P. G. 
Published: December 2006

SummarySome 200 ultramafic xenoliths and their basaltic hosts from five French localities were studied. New analyses are presented, which show the five host-rocks to be nepheline- and olivine-normative. Seven bulk analyses of xenoliths from four localities, together with analyses of their constituent diopsides and, for six, of their orthopyroxenes, are also presented. Xenoliths from four occurrences appear to have equilibrated at pressures between about 8 to 18 kb at sub-basaltic solidus temperatures. Suites of xenoliths are chemically different. Histograms were used to determine compositions of depleted and ‘undepleted’ upper mantle. A suite of peridotite xenoliths from the Bult-fontein kimberlite pipe is no less depleted in fusible oxides than xenoliths from two French localities. ‘Undepleted’ upper mantle is very similar to ‘pyrolite’ in composition, except that the latter has much higher TiO2, Na2O, and K2O contents. No xenolith encountered in this work has a bulk composition that could yield more than 12% oceanic tholeiite on partial melting.
Anorthosite—first occurrence in Nigeria and relevance to Younger Granite genesis
Authors: Wright J. B. 
Published: December 2006

SummaryPlagioclase crystal fragments and a block of anorthosite occur in small basaltic dykes on the Jos Plateau. The anorthosite is unusual, for the feldspar is labradoritic, but the interstitial mineralogy is granitic rather than basic, displaying granophyric intergrowths in places. The anorthosite is probably not an intermediate stage in fractionation from a basic parent magma towards granite, since over 95 % of this large province is granitic and the volume of basic magma required would be prohibitively large. Nor did it develop as an intermediate stage in fractionation from a salic parent magma, e.g. syenite, because the plagioclase is too calcic to have crystallized from a syenitic melt. Basic to intermediate dykes are numerous though volumetrically insignificant in the Younger Granite province. The anorthosite may be related to the evolution of small volumes of basaltic magma, which had little to do with Younger Granite magmatism.