bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of minerals from the pegmatites of the Nellore mica-belt, Andhra Pradesh, India Part III—Biotite
Authors: Babu V. R. R. M. 
Published: December 2006

SummaryThe biotites in the pegmatites are Fe2+ type. X-ray analyses indicated that they are 1M or 3T polymorphs. In the colour of the biotite iron plays an important role. From the Fe/(Fe+Mg) ratios, the analysed biotites are assumed to have crystallized between 760 and 500 °C.
On the X-ray identification of amblygonite and montebrasite
Authors: Moss A. A. , Fejer E. E. , Embrey P. G. 
Published: December 2006

SummaryPrevious investigations have been confined to individual members or to small compositional ranges of the amblygonite-montebrasite series. The present study is a survey based on twenty-two specimens in the range Amb14Mon86 to Amb92Mon8 (1·8–11·8 % fluorine), and indicates that the fluorine content may be related both qualitatively and quantitatively to differences in the X-ray powder patterns. Fully indexed powder data to d = 1·68 Å and derived cell parameters are given for four members of the series. There is no evidence of a break in the continuity of the series. The first British occurrence of both amblygonite and montebrasite is reported from a pegmatite vein in aplite at Meldon, Okehampton, Devonshire.
Staringite, a new Sn–Ta mineral from north-eastern Brazil
Authors: Burke E. A. J. , Kieft C. , Felius R. O. , Adusumilli Maria S. 
Published: December 2006

SummaryStaringite, (Fe,Mn)0·5(Sn,Ti)4·5(Ta,Nb)1·0O12, occurs as inclusions in tapiolite from pegmatites at Seridózinho and Pedra Lavreda, Paraiba State, NE. Brazil. An indexed powder pattern is presented. The mineral is tetragonal with a 4·742 Å and c 9·535 Å, and most probably has a ‘trirutile’ structure. Electron-microprobe analysis yielded Ta2O5 21·5%, Nb2O5 1·8, SnO2 73·3, TiO2 0·03, FeO 3·7, MnO 0·3, sum 100·6%. Dcalc 7·17. Micro-indentation hardness (load 100 g) 1033–1187 kg/mm2; reflectivity at 470 nm (R0) 12·8 to (R′e) 14·5%, at 546 nm 12·1–13·9, at 589 nm 12·0–13·7, and at 650 nm 11·8–13·6; staringite is uniaxial positive.
Harmotome from the Tokatoka district, New Zealand
Authors: Black Philippa M. 
Published: December 2006

SummaryHarmotome, associated with analcime, is described from andesite dykes at Rehia and Maungarahu in the Tokatoka district, New Zealand. The Maungarahu harmotome has the composition: (Na1·03K0·23)(Ba1·54Ca0·18)Al4·66Si11·31 12·39 H2O; physical properties: α 1·498, β 1·503, γ 1·506, 2Vγ 75–82° β:[001] 28° D 2·378; and cell constants: a 9· 906±0·006, b 14·119 ±0·003, c 8·712±0·007 Å, β 124° 57′ ± 3′. The harmotome is Ba-poor, and 2 Na+ has substituted for Ba2+ on a valency basis. Analcime associated with the Maungarahu harmotome has chemical composition: (Na15·16 K0·03Ca0·09)Al15·52Si32·47 15·93 H2O and physical properties: n = 1·483, D = 2·257, a = 13·708 Å. The zeolites are believed to have crystallized from Na and Ba-rich alkaline solutions at approximately 200°C The source of the Ba is baryte concretions in adjacent limestones.
Formation of the hour-glass structure in augite
Authors: Strong D. F. 
Published: December 2006

SummaryA study of augite in over three hundred thin sections of mainly alkalic rocks permits the distinction of two main types of hour-glass structure. The common ‘swallow-tailed’, sometimes skeletal augite crystals are found in the fine-grained groundmass of many rock types, and it is suggested that rapid crystallization alone accounts for their formation. Hence, this type of hour-glass structure has been called ‘quench hour-glass’. The hour-glass structures of larger augite crystals of porphyritic and coarse-grained rocks are commonly described as hour-glass ‘zoning’, as they result primarily from compositional differences between the different sectors. These were formed under conditions of relatively slower cooling than the ‘quench hour-glass’, and thus cannot be explained in the same way. They are thought to have formed by a process involving adsorption of impurities on a particular crystal face so as to impede growth of these faces, producing an initial skeleton of hour-glass form, which is completed by later crystallization of augite richer in FeO, Na2O, TiO2, and Al2O3. This hypothesis also explains the patchy zoning of other augite crystals, casting doubt on some petrogenetic interpretations of such zones as core zones.
Porphyritic plagioclase–hornblende–pyroxene granulite from charnockitic rocks of Chipurupalli, Visakhapatnam district, Andhra Pradesh, South India
Authors: Rao K. S. R. , Rao A. T. , Sriramadas A. 
Published: December 2006

SummaryAn unusual occurrence of porphyritic plagioclase-hornblende-pyroxene granulite (porphyritic basic charnockite) has been observed within the ‘Charnockite region’ of the Eastern Ghats of the Precambrian formations of India. From the X-ray and chemical data the phenocrysts are considered to be augite phenocrysts. Based on petrographic and chemical evidence it is inferred that the basic charnockites of Chipurupalli area in Visakhapatnam district are formed from tholeiitic magma as a gabbroic mass under deep seated plutonic conditions. The gabbroic mass has been recrystallized as plagioclase-hornblende-pyroxene granulite due to later metamorphism, leaving most of the phenocrysts unaffected.
Cognate xenoliths in the Tertiary uhrabasic dykes of south-west Skye
Authors: Gibb Fergus G. F. 
Published: December 2006

SummaryA group of ultrabasic dykes occurring in south-west Skye is typified by often abundant and diverse ultrabasic xenoliths composed of essentially the same minerals as the dykes. The xenoliths, which vary considerably in shape and size, are in sharp contact with the host rocks and exhibit no evidence of remelting by, or reaction with, the dykes. Although extensive axial concentration of olivine occurred in the dykes during intrusion, the xenoliths appear to be randomly distributed throughout all but the extreme margins of the dykes and often exhibit a preferred orientation. The orientation and distribution of the xenoliths are attributed to the suppression of rotation and axial migration of the xenoliths during the emplacement of the dykes because of the relatively high viscosity of the suspending medium.The ultrabasic xenoliths, unlike many of those occurring in basalts, kimberlites, etc., are considered unlikely to represent primary upper mantle material and it is suggested that they were probably derived by the disintegration of layered ultrabasic rocks genetically related to the dykes and hence are of cognate origin.
Paragenesis of staurolite in pelitic
schists of Kishangarh, District Ajmer,
India
Authors: Lal R. K. , Shukla R. S. 
Published: December 2006

Summary
The staurolite-bearing schists of the area
were metamorphosed in the staurolite-kyanite zone
of the amphibolite facies. The various assemblages
of the pelitic schists are represented in the AKF
and Thompson's AFM diagrams. Within the
PT conditions of
stability of staurolite, this mineral develops in
pelitic schists that have a high
Al2O3
(excess)/(K2O+FeO+MgO) ratio
so that the plots of analyses lie above the
muscovite-garnet join in the AKF diagram. The
three-phase field of staurolite-kyanite-biotite in
the AFM diagram migrates towards the lower FeO/MgO
side with increasing oxidation ratio and thus
staurolite-bearing rocks are not necessarily
restricted to pelitic schists with high FeO/MgO
ratio as is commonly believed. On the other hand,
the three-phase field shifts towards the higher
FeO/MgO side with increasing grade of metamorphism
assuming oxidation ratio and pressure to be
constant, thus reducing the composition field of
staurolite schists in the AFM diagram.
On the electrolysis of basalt, II:
experiments in an inert atmosphere
Authors: Oppenheim M. J. 
Published: December 2006

Summary
The recently described electrolysis of
molten basalt (Oppenheim, 1968) gave indefinite
results with regard to the behaviour of iron.
Repeating the experiments in an inert atmosphere
has shown that ferric iron moves towards the
anode, and ferrous iron to the cathode. All
metallic ions of valency three and more are now
seen to be concentrated towards the anode, with
relative enrichments in decreasing order:
Fe3+, P, Ti, Si, and Al; and
oxygen gas is released at the anode. Metals of
valency one and two are concentrated towards the
cathode with relative enrichments in decreasing
order: Na, Fe2+, K, Ca, Mn,
and Mg.
The series expected to be differentiated
within a magma consequent upon its electrolysis is
redefined. The absence of natural analogues
suggests either the non-operation of suitable
electric currents within magmas, or the
destruction of their effects by convection,
fractional crystallization, or both. An
electrolytic process is feasible at the
mantle-core boundary, leading mainly to deposition
of iron on the core and release of oxygen
upwards.
Reactions in the system
CaO-MgO-SiO2-H2O.
Hydrothermal treatment of some compositions on the
joins
Ca3Si2O7-Mg3Si2O7
and
Ca2SiO4-Mg2SiO4
Authors: Speakman K. 
Published: December 2006

Summary
The effects of hydrothermal treatments on
gel mixtures and synthetic minerals in the
C3S2-M3S2
and
C2S-M2S
regions of the CaO-MgO-SiO2
system have been investigated. The products formed
in the temperature range 180-350°C at pressures up
to 220 N/mm2 were identified.
The reactants generally behaved as simple mixtures
of binary silicates and their products agreed well
with existing data for reactions in the
CaO-SiO2-H2O
and
MgO-SiO2-H2O
systems. An unidentified phase that resulted from
the hydration of åkermanite could be a new
compound in the quaternary
CaO-MgO-SiO2-H2O
system. There was no evidence to indicate that a
magnesium analogue of kilchoanite can be formed
from materials that are isostructural with
γ-Ca2SiO4.
Optical data on some authigenic feldspars
from Western Australia
Authors: Glover J. E. , Hosemann P. 
Published: December 2006

Summary
Authigenic envelopes up to 0·18 mm thick
on clastic potassium feldspar grains from arkoses
and subgreywackes of the Devonian Nannyarra
Greywacke have been examined with the four-axis
universal stage. The plane of the optic axes is
parallel to (010) in some segments of individual
envelopes and normal to (010) in others, and the
range of 2Vα over all
envelopes is from close to 0° to 65°. The optics
are ascribed to modifications of potassium
feldspar corresponding to high-and low-sanidine
and orthoclase.
The Mössbauer spectra of several micas and
related minerals
Authors: Hogg C. S. , Meads R. E. 
Published: December 2006

Summary
Well-resolved Mössbauer spectra of several
dioctahedral and trioctahedral micas have been
obtained and subjected to detailed computer
analysis. Most of the spectra can be resolved into
two ferrous quadrupole doublets and one ferric
quadrupole doublet. In dioctahedral micas, ferrous
iron is seen to occupy the larger, more symmetric
octahedral site in preference to the smaller, less
symmetric site, confirming predictions made on the
basis of structure alone. In trioctahedral micas
there is still a tendency for ferrous iron to
occupy preferentially the more symmetric
octahedral site even though the two octahedral
sites are no longer distinguished by size. A
lithium-rich biotite gives a spectrum typical of
that expected from a mica with a zinnwaldite
structure, but the spectrum of a more
authenticated zinnwaldite could not be resolved
sufficiently for detailed structural
interpretation. The spectra of pyrophyllite and
talc give results that can be related to the
corresponding micas by considering their
respective structural differences. In none of the
micas studied was there evidence of ferric iron in
tetrahedral coordination. The ferrous: ferric
ratios obtained from the Mössbauer spectra do not
always agree with the chemical values. In several
cases the spectra show more ferrous iron than
found chemically. It is suggested that the
spectral values are more accurate, oxidation on
chemical analysis being the most likely source of
error.
Grandidierite from Cuvier Island, New
Zealand
Authors: Black Philippa M. 
Published: December 2006

Summary
Grandidierite has been found in hornfelses
around a diorite stock on Cuvier Island. Physical
properties and electron microprobe analyses are
given for two Cuvier Island and two Madagascan
grandidierites. The Cuvier Island grandidierite
has crystallized under conditions of the
K-feldspar-cordierite hornfels facies at
temperatures of approximately 600°C. and pressures
(Pload) of less than 300
bars.
On the occurrence of varlamoffite at the
Sardine tin mine, North Queensland,
Australia
Authors: Taylor R. G. , Morgan W. R. , Phillips D. N. 
Published: December 2006

Summary
A new occurrence of varlamoffite is
described, and the results of chemical analysis,
differential thermal analysis, and infra-red
spectrographic analysis are presented. It is
suggested that varlamoffite is of secondary origin
resulting from the attack of meteoric waters on
stannite.
Pyroxenes from non-carbonaceous chondritic meteorites
Authors: Binns R. A. 
Published: December 2006

SummaryChemical, optical, and X-ray data are presented for pyroxenes from a representative selection of chondrites. The Mg-Fe pyroxenes originally crystallized above 1000-1200 °C as the protoenstatite-protohypersthene polymorph, and inverted on cooling to the polysynthetically twinned clinoenstatite-clinohypersthene polymorph. In most chondrites the latter became converted to orthopyroxene during recrystallization at temperatures ranging up to 900 to 950 °C. The contents of certain minor elements changed during the clino-ortho inversion. Ancestral protoenstatiteprotohypersthene may have been slightly non-stoichiometric. Accessory Ca-rich pyroxenes are discussed briefly.
Pyroxene and biotite from the charnockitic rocks of Garbham area, Srikakulam district, Andhra Pradesh, India
Authors: Bhattacharyya C. 
Published: December 2006

SummaryChemical analyses and optical properties of ten orthopyroxenes, two clinopyroxenes, and six biotites (partial analyses) are presented from basic to intermediate charnockites of the Garbham area. The orthopyroxene is hypersthene to ferrohypersthene and the clinopyroxene is sahlite. Biotite has secondarily formed from pyroxene, particularly orthopyroxene, as a result of injection of potassic fluid in the basic charnockite. By combining the data of Srikakulam with those from other areas of the world it is shown that during the transformation of pyroxene to biotite in charnockitic rocks, in general, Mg and Fe2+attain near-equilibrium distribution between orthopyroxene and biotite as well as between clinopyroxene and biotite. The magnesium distribution coefficient (KD) of coexisting orthopyroxene and biotite is found to increase with the increase of temperature of biotite formation. A tentative geothermometric scale has been proposed plotting temperature of biotite formation against magnesium distribution coefficient of coexisting orthopyroxene and biotite. According to this scale, biotite in basic and semibasic charnockites from Garbham has formed between 285 and 465 °C.
Application of the muscovite-paragonite geothermometer to a staurolite-grade schist from Sulitjelma, north Norway
Authors: Henley K. J. 
Published: December 2006

SummaryThe occurrence of coexisting paragonite (containing 0·70 % CaO) and muscovite (containing 0·16 % CaO) in a staurolite-grade paragonite-muscovite-hornblende-garnet-biotite schist from Sulitjelma enables an estimate to be made of the temperature of recrystallization, using an extension, based on crystal chemistry considerations and available analyses of muscovites and paragonites from metamorphic rocks, of the experimentally determined solvus in the K-Na white mica system into the Ca-K-Na system. This temperature of recrystallization is approximately 550–70 °C and is consistent with the experimental data on the coexistence of staurolite and quartz in the system Fe-A1-Si-O-H (Richardson, 1968).
Russellite: a second occurrence
Authors: Hodge L. C. 
Published: December 2006

SummaryRussellite Bi2O3. WO3 occurs in a small pegmatite near Poona, Western Australia. The fine-grained yellow to pale green material is an inseparable mixture of russellite, bismite, koechlinite, and bismutite. X-ray powder diffraction, physical, and chemical data agree in general with the original description of the mineral from Cornwall, England. The original analyses made on micro quantities are now supplemented by analyses on macro quantities.
The initiation of crystal growth in glasses
Authors: Rogers P. S. 
Published: December 2006

SummaryThe application of classical nucleation theory to the initiation of crystal growth in glasses is discussed. Its application to experimental results obtained for the rate of nucleation in three types of glass, one showing nucleation separately from crystal growth, another showing simultaneous nucleation and growth, and the third showing crystal growth after metastable liquid/liquid phase separation, is then described. Recent work on the kinetics of unmixing in glasses is outlined. The influence of so-called ‘nucleating agents’ in the glasses described appears to be exerted through changes in the anionic structure.
The kinetics of crystal growth in an aluminosilicate glass containing small amounts of transition-metal ions
Authors: Williamson J. 
Published: December 2006

SummaryQuantitative data are presented for the kinetics of crystal growth in an aluminosilicate glass to which a few wt % of a transition-metal oxide had been added. The composition of the base glass was CaO 3o, MgO 2, Al2O3 15, SiO2 53 wt %, to which the oxides of iron, vanadium, chromium, or zinc were added. Glasses were prepared with a range of high to low valency ratios in cases where the transition metal oxide could exist in two or more oxidation states.Small quantities of Fe2+, Fe3+, Zn2+, V3+, V4+, and V5+ were all found to increase the kinetics of crystal growth from the glass phase. The magnitude of the effect is compared with additions of Mg2+ to the glass. Cr2+, Cr3+, and Cr6+ were found to decrease the rates of crystal growth. Values for the apparent activation energy for crystal growth ranged from ∼50 kcal/mole to ∼150 kcal/mole. The high values were found to be of the same order of magnitude as that for the activation energy for viscous flow in the glass at the crystallization temperature.The results are interpreted in terms of the structure of the glasses and current theories on the rate of crystallization of glasses.
Nucleation and growth of iron oxides in olivines, (Mg,Fe)2SiO4
Authors: Champness P. E. 
Published: December 2006

SummaryIron-rich olivines have been oxidized in air in the laboratory and the mechanism of their breakdown has been elucidated using X-ray diffraction and electron microscopy. Low-temperature oxidation (500–800 °C) produces well-oriented hematite- and magnetite-like precipitates together with amorphous silica. The reaction is a cellular one in which thin needles of oxide about 50–100 Å apart grow into the matrix separated by regions of amorphous silica. Nucleation of spherical colonies of the iron oxide and silica occurs on dislocations.Although the hematite or magnetite always shows the same topotactic relationship with the matrix, the direction in which the needle-like precipitates grow is determined by the orientation of the nucleating dislocation. The small size and highly distorted nature of these precipitates accounts for the diffuseness of their X-ray reflections.Oxidation at 1000 °C produces undistorted equiaxed grains of the oxides about 0·2 μm in size. They are surrounded by silica, which produces a disordered electron diffraction pattern. As the temperature is raised, the silica achieves more structural order and the oxide grains increase in size.
Rotational fabrics in metamorphic minerals
Authors: Powell Derek , Treagus J. E. 
Published: December 2006

SummaryA model has been constructed that establishes the geometry of inclusion fabrics to be expected in near-spherical crystals that grow continuously while either the crystals rotate in a static matrix or a matrix fabric rotates about them. Garnets in certain metamorphic rocks contain inclusion fabrics whose geometry is very similar to that of the model. Such syntectonic, snowball, or rotational garnets, as they have previously been termed, can be studied in three dimensions. A method is outlined whereby the rotation axes for individual crystals viewed in thick sections can be located in certain planes of cut. The significance of the geometry of included rotational fabrics is discussed in relation to previous work and to possible mechanisms of rotation.
Exsolution during metamorphism with particular reference to feldspar solid solutions
Authors: Sturt Brian A. 
Published: December 2006

SummaryIn the aureole of the syn-orogenic Hasvik Gabbro a variety of exsolution phenomena developed during the contact metamorphism. These exsolution phenomena have similar textures to those produced during the age-hardening of metal alloys. In feldspars the exsolution precipitates are closely related to the pattern of excesses over and deficiencies from the formula requirements, particularly in terms of SiO2 and Al2O3. The exsolution products are dependent upon both the temperatures of ageing and the details of the mineral chemistry. Evidence supporting an exsolution theory of origin for myrmekite is provided, and it is shown that precipitation from heterotype feldspar solid solutions during metamorphism may in fact be a complex process involving a number of precipitate phases.The nucleation of sillimanite as a precipitate phase is discussed and it is shown how sillimanite develops at a number of distinctive sites within feldspar and garnet. From the textural relations of sillimanite precipitates and their host minerals a control exerted by the thermal stress configuration over the nucleation of precipitate phases is suggested. It is argued that the thermal stresses exerted across grain boundaries and within minerals during metamorphism may have considerable relevance to the interpretation of textures in metamorphic rocks.
Experimental modification of naturally deformed galena crystals and their grain boundaries
Authors: Stanton R. L. 
Published: December 2006

SummaryIt is now well established that naturally—occurring sulphides—particularly galena—are frequently found in the deformed state and that at least part of this deformation can be eliminated by annealing in the laboratory.The present contribution is concerned principally with galena, for which it is indicated: that tectonic deformation leads to natural work hardening, which may be reduced by simple heating in vacuo; that the rate of softening is related to the annealing temperature; that softening is related to recovery at low temperatures and to both recovery and recrystallization above 250–300 °C that single crystals of galena exhibiting minor slip and kinking recrystallize yielding new, unstrained grains elongated parallel to the old slips and kinks, i.e. a foliation involving unstrained grains may form under a regime devoid of compressive stress; and that where deformed galena and deformed sphalerite coexist, the galena may be made to recrystallize completely (e.g. at 325 °C in 50 days) while leaving the deformation in the sphalerite entirely intact; apparently the coexistence of a strained component A and an unstrained component B in a deformed ore or other metamorphic rock does not necessarily indicate differences in age or deformational history—it may simply indicate that post-deformational temperatures have exceeded the recrystallization temperature of one component but not of the other.