bluuebunny/crossref_metadata_2025 huggingface dataset:
An in-situ high-temperature structural study of stable and metastable CaAl2Si2O8 polymorphs
Authors: Daniel I. , Gillet P. , McMillan P. F. , Richet P.
Published: December 2006

High-temperature Raman spectroscopy and optical microscopic observations have revealed a new metastable polymorph of CaAl2Si2O8 composition, which brings to four the number of known crystalline phases in this system. Similar to the metastable monoclinic pseudo-orthorhombic and pseudo-hexagonal phases, the new polymorph nucleates prior to anorthite, at around 1545 K, and its pseudo-liquidus temperature is 1700 ± 10 K. It can also be formed from the transformation of the pseudo-hexagonal phase at 1050 K. The actual structure of this new crystalline form is unknown, but its Raman spectrum indicates that it is most likely a 6-membered alumino-silicate framework. We have obtained all three metastable phases as pure single crystals using wire loop heating techniques, and have studied their structures via Raman spectroscopy up to their metastable melting points or transformation temperatures.
Investigation of Al,Si order in K-feldspars using 27Al and 29Si MAS NMR
Authors: Xiao Yuehui , James Kirkpatrick R. , Hay Richard L. , Kim Youn Joong , Phillips Brian L.
Published: December 2006

This paper presents a 27Al and 29Si MAS NMR study of K-feldspars and demonstrates that the spectra are sensitive to variations in the state of Al,Si order. For synthetically annealed samples, the results are in agreement with previous IR spectroscopy (Harris et al., 1989) and demonstrate that Al,Si rearrangement continues after the samples have become monoclinic as determined by powder XRD. NMR methods provide a significantly improved picture of the state of local Al,Si order in such samples. For triclinic samples, measures of the state of Al,Si order (M1 and M2 of 27Al spectra and M2 of 29Si spectra) correlate well with site occupancies determined by powder XRD, but for the monoclinic samples the NMR parameters continue to change whereas the XRD parameters do not. Interpretations based on the NMR results for the synthetically disordered samples are consistent with 1-step disordering, as observed by XRD. 27Al and 29Si MAS NMR is likely to be a useful tool for probing the state of local Al,Si order in a wide variety of natural samples.
Exsolution and alteration microtextures in alkali feldspar phenocrysts from the Shap granite
Authors: Lee Martin R. , Waldron Kim A. , Parsons Ian
Published: December 2006

Alkali feldspar phenocrysts (bulk composition Or75.0Ab24.6An0.4) in the subsolvus Shap granite comprise a fine-scale mixture of subregular pristine crypto- and micro-perthites with altered, micropore-rich feldspar with irregular microstructures. The regular perthites are strain-controlled intergrowths of Albite and/or Periclinetwinned albite exsolution lamellae within tweed orthoclase. The microperthites formed at ⩽ 590°C by heterogeneous nucleation of thin albite films which coarsened to > 1 µm length. Cryptoperthites developed at < 400°C by homogeneous nucleation of sub-µm long platelets between films. Platelets are coherent, but the coarser microperthite lamellae are semi-coherent, with pairs of misfit dislocations sub-regularly spaced along the albite-orthoclase interface. As much as 30% of any one feldspar crystal is turbid, a result of the formation of numerous µm to sub-µm sized micropores during deuteric alteration. In some areas, deuteric fluids gained access to the interior of feldspar crystals by exploiting semi-coherent film lamellae. Albite was selectively dissolved and micropore-rich irregular microcline was reprecipitated in its place. In other parts of the feldspars deuteric recrystallization completely cross-cuts the pristine microtextures and patch perthites have formed. These are coarse, incoherent to semi-coherent intergrowths of irregular microcline (replacing tweed orthoclase) and Albite-twinned albite. The deuteric reactions occurred at < 400°C; the main driving force for dissolution and reprecipitation was decrease in the elastic strain energy at the coherent interfaces of crypto-and micro-perthite lamellae, and the recrystallization of tweed orthoclase to irregular microcline.
Significance of ultrahigh-P talc-bearing eclogitic assemblages
Authors: Liou J. G. , Zhang R. Y.
Published: December 2006

Talc was identified as an equilibrium associate of omphacite, kyanite, zoisite, and garnet in some coesitebearing eclogites and as a retrograde phase in associated garnet peridotite from the Bixiling mafic-ultramafic complex in the Dabie ultrahigh-P metamorphic terrane, central China. Observed talc- and tremolite-bearing assemblages within the coexisting mafic and ultramafic rocks together with established phase relations for the simple system CaO-MgO-Al2O3-SiO2-H2O constrain the P-T path for retrograde metamorphism. This, together with reported talc occurrences from the Dora Maira massif, leads to the conclusion that UHP talc assemblages are confined to mafic and pelitic rocks of unusual chemistry, and are not stable at ultrahigh pressures in ultramafic rocks. Thus, talc cannot be an important H2O-bearing phase in deep mantle ultramafic rocks.
Nanometre scale textures in agate and Beltane opal
Authors: Lu Taijing , Zhang X. , Sunagawa Ichiro , Groves G. W.
Published: December 2006

We have carried out TEM observations of agates of geode origin and Beltane opals. Optically observable individual fibres in agates are composed of many fine fibres which consist of quartz crystallites of 8 to 100 nm in length stacked together parallel to <110> or <100> with c-axes perpendicular to the fibre elongation. The optically observable systematic striations in agate are found to consist of cyclic alternation of layers due to variation in grain size and porosity. Large quartz crystals, protruding into the spaces of geodes, represent the last stage of formation of these bands, and are merely a continuation of the banding sequence. Nanometre scale textures of cristobalite fibres were revealed in Beltane opals. The cristobalite crystallites have the size of 3 to 20 nm in length and are also stacked together. Our TEM results suggest that embryonic particles were formed in their corresponding growth environments and agglutinated to form fibres.
Relationship between the crystallographic orientation and the ‘alexandrite effect’ in synthetic alexandrite
Authors: Liu Yan , Shigley James E. , Fritsch Emmanuel , Hemphill Scott
Published: December 2006

The transmittance spectra of a synthetic alexandrite recorded along directions parallel to the three crystallographic axes are generally similar, but the observed colour changes along these directions under different light sources are quite different. Calculated hue-angle changes for the colours observed under different pairs of C.I.E. standard illuminants are the largest for light travelling parallel to the a-axis. Therefore, alexandrite should be cut as a gemstone with the top facet oriented parallel to (100) for it to show the most dramatic change in colour.
Morimotoite, Ca3TiFe2+Si3O12, a new titanian garnet from Fuka, Okayama Prefecture, Japan
Authors: Henmi Chiyoko , Kusachi Isao , Henmi Kitinosuke
Published: December 2006

Morimotoite, Ca3TiFe2+Si3O12, has been found in contaminated rocks which are considered to be a kind of endoskarn at Fuka, Bitchu-Cho, Okayama Prefecture, Japan. Morimotoite is derived from andradite, , by the substitution Ti + Fe2+ = 2Fe3+. It is associated with calcite, vesuvianite, grossular, wollastonite, hematite, prehnite, fluorapatite, perovskite, zircon, baddeleyite and calzirtite. It is cubic with space group Ia3d. The unit cell dimension a is 12.162(3) Å. Its refractive index n is 1.995(2) and the density 3.75(2) g cm−3 (meas.), 3.80 g cm−3 (calc.). The Mohs' hardness is 7.5. Calculation of the analytical data on the basis of twelve oxygen atoms and eight cations shows that this mineral has a simplified chemical formula Ca3(Ti,Fe2+Fe3+)2(Si,Fe3+)3O12 where Ti > Fe2+ > 0.5. Morimotoite was synthesized at low oxygen fugacities, 650 and 700°C and 1 kbar total pressure.
The Shiant Isles Main Sill: structure and mineral fractionation trends
Authors: Gibb F. G. F. , Henderson C. M. B.
Published: December 2006

The Shiant Isles Main Sill, of Tertiary age, is a classic example of a composite, differentiated alkaline basic sill. The first unit to be intruded was a 2 m thick olivine teschenite which was emplaced with phenocrysts of olivine (mg > 83) [mg ≡ Mg#] and, perhaps, plagioclase. This was intruded by a 24 m thick picrite sill consisting of a mush of melt and suspended olivine phenocrysts (mg > 83) with a D-shaped modal profile. The 140 m thick picrodolerite-crinanite unit was formed by a magma carrying ∼ 10% olivine (mg > 83) as the main phenocryst phase, together with some calcic plagioclase phenocrysts, being emplaced into the top of the picrite unit before the host rock was completely solidified. The olivine phenocrysts settled towards the bottom to form the picrodolerites. In-situ differentiation processes occurred under conditions of almost perfect fractional crystallization, during which very strongly zoned ophitic crystals of olivine (fayalitic rims) and clinopyroxene (hedenbergitic rims), and zoned laths of plagioclase (anorthoclase rims), formed. The last unit consists of ∼ 2 m of granular olivine picrodolerite which was intruded into the upper crinanites, again before the host rock was fully solid.

The mineral zoning patterns are interpreted using published cation diffusion coefficient data, and used to show that the picrite unit might have cooled to the blocking temperatures for Mg and Fe diffusion in < 5 years, and that even the relatively thick crinanite unit cooled very fast, so preserving the zoned Fe-Mg olivine and pyroxene compositions. The compositions of coexisting ilmenites and spinels define a redox trend which initially lies close to fayalite-magnetite-quartz buffer conditions, but later becomes more reducing and approaches magnetite-wustite buffer conditions. The final stages of development occurred during sub-solidus deuteric processes and involved formation of analcime and zeolites, as well as localized sulphide mineralization.
Compositional cyclicity in a pyroxenitic layer from the Main Zone of the Western Bushveld Complex: evidence for repeated magma influx
Authors: Mitchell Andrew A.
Published: December 2006

Lacking the pronounced modal layering of the underlying Critical Zone, the Main Zone of the Bushveld Complex nevertheless displays well-developed cryptic layering, expressed in a series of iron-enrichment trends, each defining a unit of the order of 100 to 200 m thick. At the base of one such unit, 1100 m above the Main Zone — Critical Zone contact, a 10 m thick pyroxenitic layer was intersected in an exploration borehole from the southern sector of the western Bushveld.

Within the pyroxenitic layer, mineral chemistry defines a series of five cycles of upward Mg and Cr enrichment in pyroxenes, and Ca enrichment in plagioclase. The mineral chemistry, supported by textural evidence, suggests the influx of successive surges of magma. Sustained streaming of magma gave rise to adcumulate textures in the central portion of each cycle, with orthocumulate textures at bases and tops of cycles representing waxing and waning stages of magma surges.
Fluorine in igneous rocks and minerals with emphasis on ultrapotassic mafic and ultramafic magmas and their mantle source regions
Authors: Edgar A. D. , Pizzolato L. A. , Sheen J.
Published: December 2006

In reviewing the distribution of fluorine in igneous rocks it is clear that F abundance is related to alkalinity and to some extent to volatile contents. Two important F-bearing series are recognized: (1) the alkali basalt—ultrapotassic rocks in which F increases with increasing K2O and decreasing SiO2 contents; and (2) the alkali basalt—phonolite—rhyolite series with F showing positive correlation with both total alkalis and SiO2. Detailed studies of series (1) show that F abundance in ultrapotassic magmas (lamproite, kamafugite, lamprophyre) occurs in descending order in the sequence phlogopite>apatite>amphibole>glass. Fluorine contents in the same minerals from fresh and altered mantle xenoliths may be several orders of magnitude less than those in the host kamafugite. For many lamproites, F contents correlate with higher mg# suggesting that F is highest in the more primitive magmas.

Experiments at mantle conditions (20 kbar, 900–1400°C) on simplified F-bearing mineral systems containing phlogopite, apatite, K-richterite, and melt show that F is generally a compatible element. Additionally, low F abundance in minerals from mantle xenoliths suggests that F may not be available in mantle source regions and hence is unlikely to partition into the melt phase on partial melting. Melting experiments on the compositions of F-free and F-bearing model phlogopite harzburgite indicate that even small variations in F content produce melts similar in composition to those of lamproite.
Bromine geochemistry of british groundwaters
Authors: Edmunds W. M.
Published: December 2006

The concentrations of Br in potable groundwaters in the United Kingdom range from 60 to 340 µg 1-1. The occurrence of Br is described in terms of the Br/Cl weight ratio which enables small changes in bromide concentrations to be assessed in terms of salinity. Median values of Br/Cl in groundwaters range from 2.60 to 5.15 × 10−3 compared with a sea water ratio of 3.47× 10−3. In recent shallow groundwaters the Br/Cl ratio is rather variable in response to a range of natural and anthropogenic inputs (marine and industrial aerosols, industrial and agricultural chemicals including road salt). Some slight enrichment in Br/Cl also occurs naturally during infiltration as a result of biogeochemical processes.

Evolution of Br/Cl along groundwater flow lines reflects the sources of increasing salinity; either the influence of marine sedimentary formations or evaporites. The groundwaters in the Triassic sandstones of the English Midlands show significant Br depletion due to the evaporite source, in contrast to groundwaters in Cumbria. Br/Cl ratios in the Sherwood Sandstone of the East Midlands mainly reflect the natural input sources and can be used to help understand the palaeohydrology.
Variations in F and Cl contents in apatites from magnetite—apatite ores in northern chile, and their ore-genetic implications
Authors: Treloar Peter J. , Colley Howard
Published: December 2006

Magnetite—apatite deposits associated with the Atacama Fault Zone of northern Chile are interpreted here, on field criteria, as being the products either of hydrothermal fluids with a strong magmatic signature, or of late-stage Fe-rich magmas mixed with an aqueous fluid. Even in the Chilean iron belt, apatite-rich magnetite deposits are a rarity. Variations in F- and Cl- contents in apatites, strongly zoned with respect to halogens, are indicative of primary variations in fHF and fHCI in the hydrothermal fluids. Small variations in halogen fugacities in the aqueous fluid are capable of buffering large variations in halogen content within apatite crystals in equilibrium with that fluid. The recorded halogen zonation profiles are inconsistent with crystallization of the apatites simply from a volatile-rich, late-stage fractionation Fe-rich magma, or its derived magmatic vapour. It is more likely that they are the result of mineral—fluid buffering with a fluid that represents the mixing of a magmatically-derived aqueous fluid with a meteoric fluid that has variably scavenged Ca and Cl from within the country rocks. The source magma of the former is probably an Fe-P enriched acidic magma, derived by fractionation of primary calc-alkaline basic magmas.
Fluvial metal transport near sources of acid mine-drainage: Relationships of soluble, suspended and deposited metal
Authors: Boult Stephen
Published: December 2006

The Afon Goch (Anglesey, UK) is a short (12 km source to estuary) stream highly contaminated by acid mine drainage (AMD) throughout its length, due to past-mining at the head of the stream. Metal distribution is strongly controlled by the pH, which increases downstream particularly at confluences with two unpolluted tributaries. A pH increase causes precipitation of metals, primarily Fe as hydroxide, thus altering the transport of the metal load, potentially allowing storage of metal within the river as deposited material. However, further work suggests that the controls on whether metal can behave non-conservatively, and therefore the controls on metal distribution, are more complicated than being purely pH dependent. This is because much of the Fe load, even at the low pH at the head of the stream, is not soluble Fe3+ but colloidal Fe hydroxide. Consequently, coagulation is a requisite intermediate step between precipitation and potential for settling. It is possible that in reaches of the stream away from tributary confluences, the process of coagulation is the predominant influence on metal distribution. Furthermore, because much of the metal load in the water column is very fine, its deposition results in a sediment in which the metals can be intimately associated with a biofilm at the sediment/water interface. Such associations change both deposition and erosion characteristics of the sediment and have implications for subsequent diagenesis and mineral morphology.
Synthetic armalcolite and pseudobrookite
Authors: Medvedev A. Ya.
Published: December 2006

Armalcolite and pseudobrookite have been crystallized from synthetic melts of basaltic composition with variable amounts of added TiO2. It was found that the composition of the armalcolite and pseudobrookite are dependent on the TiO2 content of the melt and the conditions (particularly oxygen fugacity, but also temperature and quenching rate) of formation. The maximum Al2O3 content of pseudobrookite appears to be ∼14–15 wt.% Al2O3, a spinel-like phase being exsolved at higher Al2O3 concentrations. Generally armalcolite is formed at low pO2 and pseudobrookite at higher oxygen fugacities.
Crystal chemistry of danalite from Daba Shabeli Complex (N Somalia)
Authors: Nimis P. , Molin G. , Visonà D.
Published: December 2006

Danalite is the Fe2+ end-member of the minerals of the helvite group, which have the general formula M8(BeSiO4)6S2, with M = (Mn,Fe2+,Zn). These minerals are relatively uncommon, although limited amounts are known at many localities round the world (e.g. Ragu, 1994; Larsen, 1988; Kwak and Jackson, 1986, and references therein). Their typical host rocks are skams, but occurrences in mineralized veins pegmatites, and altered alkali granites have also been reported. Danalite is rarer than helvite (Mn endmember) and genthelvite (Zn end-member) and, unlike the other two end-members, has never been found nor synthesized as a pure mineral (Mel'nikov et al., 1968).
Clinobisvanite, eulytite, and namibite from the pala pegmatite district, San Diego Co., California, USA
Authors: Foord Eugene E.
Published: December 2006

The 100 Ma complex LCT-type composite pegmatite- aplite dykes, intruded into various units of the Southern California Batholith, are known to contain bismuth minerals. Jahns and Wright (1951) reported the following primary and secondary bismuth minerals from the quartz-rich cores of a number of dykes in the Pala district, San Diego Co., California: native bismuth, bismuthinite, bismite, bismutite, and beyerite.
Cadmium substitution in miargyrite (AgSbS2) and related phases: an experimental reconnaissance
Authors: Kelleher I. , Redfern S. A. T. , Pattrick R. A. D.
Published: December 2006

An experimental study of cadmium substitution into AgXS2 phases (X = As, Bi, Sb) indicates significant amounts of cadmium can be incorporated in the structure by the mechanism 2Cd ⇌ Ag + X. The limit of substitution of Cd in the high-temperature polymorph of miargyrite, β-AgSbS2 is 6.2 at.%, whereas the low-temperature polymorph, α-AgSbS2, can accommodate at least 12 at.% cadmium. Substitution of Cd into the cubic β-AgSbS2 induces a small monoclinic distortion and the unit cell becomes pseudo-cubic. The α ⇌ β transition in Cd-substituted miargyrites is modified by the solute ions, with both a reduction of Tc and transition smearing evident. Similar effects are also recorded in Cd-substituted AgAsS2 and AgBiS2.
Transition metal rutiles and titanates from the Deadhorse Creek diatreme complex, northwestern Ontario, Canada
Authors: Platt R. Garth , Mitchell Roger H.
Published: December 2006

The main mineralized zone of the West subcomplex of the Deadhorse Creek diatreme complex, northwestern Ontario possesses an exotic mineralogy. Mineralization involves the first-order transition metals (principally Sc, Ti, V, Cr, Mn, and Fe), the second-order transition metals (principally Zr and Nb), the lanthanides, the actinides (principally Th and U), Be, Ba and Sr. Minerals include phenacite, zircon, uraninite, thorite, monazite-(Ce), xenotime-(Y), barylite, thortveitiite, hollandite, tyuyamunite, a number of unknown and as yet undescribed species, and those minerals more specifically described in this paper. These are Cr-V-Nb rutile, V-rich members of the crichtonite series, and a titanate of general composition (Cr,V3+,Fe3+)2(Ti,V4+,Nb)O5.

Similar to rutiles reported from alkaline rocks in general, the Deadhorse Creek rutiles are enriched in Cr and Nb, with the latter element attaining some of the highest recorded values. V contents are also unusually high and this element is thought to exist in both the tri- and tetravalent states.

The V-rich crichtonites are essentially vanadium analogues of crichtonite and lindsleyite. M-site Nb and V are the highest yet recorded. A-site cations are dominated by Ba and Sr with an inverse relationship together with lesser but significant amounts of Ca and Pb. Although not of upper mantle origin, they plot in the upper mantle LIMA quadrant of TiO2vs. FeO + Fe2O3 + MgO (Haggerty, 1991).

(Cr,V3+,Fe3+)2(Ti,V4+,Nb)O5 is thought to be a member of an homologous series of type (Cr,V3+,Fe3+)2p(Ti,V4+,Nb)2p+qO5p+4q with p = 1 and q = 0 and a V3O5-type structure. Whether this structure is ultimately derived from that of rutile or from α-PbO2 by crystallographic shear is not known.

The rutiles and titanates discussed here are thought to have formed from hydrous alkaline solutions which have scavenged the necessary elements from a mafic/ultramafic source. The origin of the solutions is not specifically known although the magmatic activity associated with the spatially related Coldwell alkaline complex and/or the Prairie Lake complex are both potential sources. Both complexes contain the necessary mafic/ultramafic rocks.
Ba-rich micas from the Yindongzi-Daxigou Pb-Zn-Ag and Fe deposits, Qinling, northwestern China
Authors: Jiang Shao-Yong , Palmer M. R. , Li Yan-He , Xue Chun-Ji
Published: December 2006

Electron-microprobe analyses of muscovite, biotite, and feldspar are reported for the stratiform Yindongzi—Daxigou Pb—Zn—Ag and Fe deposits of Qinling, northwestern China. The micas are characterized by high Ba levels in banded albite-carbonate rocks that host the deposits. The biotite is also rich in Cl, as is biotite in the nearby Tongmugou Pb-Zn deposit, although biotite and muscovite from this deposit lack Ba enrichment. It is likely that the Ba-rich micas in the Yindongzi-Daxigou deposits formed contemporaneously from the diagenesis and/or regional metamorphism of hydrothermally altered clay minerals, with the barium being derived from entrained pore fluids that may represent relict hydrothermal fluids associated with ore deposition. During the formation of coexisting muscovite and biotite, barium is preferentially partitioned into muscovite and chloride into biotite. Together with the presence of baryte rocks in the bedded ores, these data suggest that ore deposition in the Yindongzi—Daxigou deposits took place in a more oxidising environment than in the nearby Tongmugou deposit. This difference is attributed to the contrasting sedimentary environments of the two deposits, with the Yindongzi—Daxigou deposits having formed under shallow, oxic conditions and the Tongmugou deposit under deeper, anoxic conditions.
Fe-bearing trioctahedral micas from Mont Saint-Hilaire, Québec, Canada
Authors: Lalonde A. E. , Rancourt D. G. , Chao G. Y.
Published: December 2006

We document the occurrence of Fe-bearing trioctahedral micas in the Poudrette quarry in the Mont Saint-Hilaire alkaline intrusion, characterize them by microprobe analysis, Mössbauer spectroscopy, X-ray diffraction, and optical measurements, describe their mineral chemistry, and discuss their petrological significance. In the nepheline and sodalite syenite, biotite and annite occur as coarse crystals characterized by low Al content (typically 2 atoms per formula unit, a.f.u.), high Mn content (typically 0.2 to 0.8 a.f.u.) and variable Fe/(Fe+Mg) values from 0.61 to 0.97. In the gabbro, biotite is less Fe-rich, has lower Mn content and high Ti content. Phlogopite is found as small metamorphic crystals in marble xenoliths within the syenite and siderophyllite occurs as large crystals in a metasomatized albitite dyke. Fe3+/Fetot values extend from 0.079 in the siderophyllite to 0.282 in a high-Fe3+ annite. All of the micas except for the phlogopite have high contents of (Fe3+)iv (∼0.13 to 0.45 a.f.u.) despite the high availability of Al in the rocks. We suggest that the high (Fe3+)iv amounts are caused by the high Mn abundance via a local structural mechanism. The great variety of mica encountered at Mont Saint-Hilaire reflects the highly heterogeneous conditions that prevailed during magmatic and postmagmatic crystallization in this intrusion.
Ultra-high pressure aluminous titanites in carbonate-bearing eclogites at Shuanghe in Dabieshan, central China
Authors: Carswell D. A. , Wilson R. N. , Zhai M.
Published: December 2006

Petrographic features and compositions of titanites in eclogites within the ultra-high pressure metamorphic terrane in central Dabieshan are documented and phase equilibria and thermobarometric implications discussed. Carbonate-bearing eclogite pods in marble at Shuanghe contain primary metamorphic aluminous titanites, with up to 39 mol.% Ca(Al,Fe3+)FSiO4 component. These titanites formed as part of a coesite-bearing eclogite assemblage and thus provide the first direct petrographic evidence that AlFTi−1O−1 substitution extends the stability of titanite, relative to rutile plus carbonate, to pressures within the coesite stability field. However, it is emphasised that A1 and F contents of such titanites do not provide a simple thermobarometric index of P—T conditions but are constrained by the activity of fluorine, relative to CO2, in metamorphic fluids — as signalled by observations of zoning features in these titanites.

These ultra-high pressure titanites show unusual breakdown features developed under more H2O-rich amphibolite-facies conditions during exhumation of these rocks. In some samples aluminous titanites have been replaced by ilmenite plus amphibole symplectites, in others by symplectitic intergrowths of secondary, lower Al and F, titanite plus plagioclase. Most other coesite-bearing eclogite samples in the central Dabieshan terrane contain peak assemblage rutile often partly replaced by grain clusters of secondary titanites with customary low Al and F contents.
The composition and origin of massicot, litharge (PbO) and a mixed oxide of lead used as a traditional medicine in the Arabian Gulf
Authors: Worthing Michael A. , Sutherland Hector H.
Published: December 2006

Lead and lead minerals have been used for medical purposes throughout human history. For example, galena was used as an eye salve in pre-Dynastic Egypt and by the ancient Indian civilisations of Mohendro-Daro and Harappa some 3200 to 2800 B.C. (Nriagu, 1983). The use of lead and other heavy metals and their compounds in Ayurveda, the Hindu system of medicine, can be traced back to the first century A.D. when Jain and Buddhist healers began to encourage the use of these substances instead of animal products (Mukherjee, 1992).
The atomic arrangement of ojuelaite, ZnFe23+(AsO4)2(OH)2·4H2O
Authors: Hughes John M. , Bloodaxe Erich S. , Kobel Kyle D. , Drexler John W.
Published: December 2006

Ojuelaite was described from its occurrence at the Ojuela mine in Mapimi, Mexico by Cesbron et al. (1981). Those authors suggested that the phase was isostructural with whitmoreite (Moore et al., 1974), a phase of interest because of the unique arrangement of Fe octaheda in its octahedral sheet.
The conditions of metamorphism of a grossular—wollastonite vesuvianite skarn from the Omey Granite, Connemara, western Ireland, with special reference to the chemistry of vesuvianite
Authors: Ahmed-Said Y. , Leake Bernard E.
Published: December 2006

The Fountain Hill skarn, which was produced by thermal metamorphism of impure limestone in the Omey Granite aureole, consists of wollastonite, calcite, grossular-andradite garnet, diopside, B-free vesuvianite and small amounts of albite, K-feldspar and quartz. Zoning in vesuvianite is, overall, independent of birefringence but oscillatory concentric zoning in the mineral is controlled mainly by Ti. In addition to extensive within-site substitutions (e.g. F for OH in the OH-sites, Fe2+ for Mg, Fe3+ for Al, Ti for Al etc. in the Y-sites), there are significant cross-site combined substitutions involving Y-X and Y-Z but not X-Z sites so that ideal solution models for this mineral are not applicable. The thermodynamic mole fraction of Hoisch (1985) is modified to account for the excess of the ΣY cations in the Y sites and can be applied to both B-bearing and B-free vesuvianites. Using the thermodynamic dataset of Holland and Powell (1990) and taking into account the existence of andalusite, sillimanite and corundum in associated pelites, leads to the conclusion that the metamorphic conditions were about 640±20°C and 3.3±0.3 kb at 0.15±0.05 XCO2.
Blueschist-to-Greenschist Transition and the P-T Path of Prasinites from the Lavrion Area, Greece
Authors: Baltatzis Emmanuel
Published: December 2006

The Lavrion area is part of the Attic-Cycladic massif. Blue amphibole analyses revealed that they are glaucophane or ferroglaucophane. Ca-amphiboles are characterized as actinolite or actinolitic hornblende. The Ps component of epidotes from the glaucophane-bearing rocks varies from 25.42–30.89%, whereas the Ps component of epidotes from the greenschist assemblages ranges from 23.81–26.88%. Chlorites show narrow compositional variations of ferromagnesian ratios (Xmg=0.48–0.53). Albites are almost pure Ab100. The Kfeldspar present has a low Ab content. The evolution of the prasinites studied is characterized by the progressive transformation of eclogite facies (?) rocks through epidote blueschists into greenschists. A P-T path for the prasinites is presented indicating epidote blueschist facies at P-T conditions of around 7.0–7.5 kbar and 300–340°C. Pressures of 4.0–4.5 kbar and temperatures around 340–360°C are estimated for the subsequent overprint in the greenschist facies. The path EBS to GS conditions followed under nearly isothermal uplift.
Distribution of boron, lithium and beryllium in ocean island basalts from French Polynesia: implications for the B/Be and Li/Be ratios as tracers of subducted components
Authors: Dostal J. , Dupuy C. , Dudoignon P.
Published: December 2006

The study focuses on the distribution of B, Be, Li, rare earth elements (REE), high-field-strength elements (HFSE), Th, U and Pb in fresh and hydrothermally altered ocean island basalts (OIB) from French Polynesia, and evaluates B/Be and Li/Be ratios as potential tracers of subducted components in the mantle. Hydrothermal solutions affecting the rocks during cooling were derived from meteoric water, sea water and magmatic fluids. The concentrations of REE, HFSE, Th and Be in the OIB were not affected by secondary processes except during advanced stages of subaerial hydrothermal alteration where saponite was a dominant secondary phase. This alteration modified the contents of these elements, changed REE patterns and produced a positive Ce anomaly. The subaerial and submarine hydrothermal alteration (T ∼ 70–100°C) may change U concentrations in OIB, whereas Pb was only marginally redistributed during alteration.

Boron was enriched during submarine and subaerial hydrothermal alteration but was not noticeably affected in basalts altered by magmatic fluids at T > 200°C. Like B, the mobility of Li during the alteration varies with fluid temperature. Lithium became enriched in the basalts during advanced stages of lower T hydrothermal alteration (<100°C). However, this element was partly removed from the rocks during higher T alteration (>200°C) by magmatic fluids. Boron, Be and Li behave as incompatible trace elements in basaltic magmas. Beryllium content in primitive mantle is estimated to be 0.07 ppm. Fresh Polynesian OIB have low abundances of B and Li and low B/Be (2–5) and Li/Be (2.5–5) ratios compared with volcanic arc rocks, marine sediments and altered oceanic crust. Various OIB including even those which have HIMU- and EM-affinities have similar overlapping B/Be and Li/Be ratios. Both B and Li are probably stripped from a lithospheric slab during subduction-related metamorphism and are, thus, not involved in deep mantle recycling. The mantle-normalized trace element abundances of MORB and OIB usually display patterns characterized by negative B, Pb and Li anomalies. The patterns of continental crust and crustal rocks have distinct positive anomalies for these elements whereas continental basaltic rocks have variable relative abundances of B, Pb and Li. The anomalies of these elements in basalts can be useful in discriminating their tectonic setting and constraining the mantle source regions of basalts.
A Model and Simulation of Branching Mineral Growth from Cooling Contacts and Glasses
Authors: Fowler Anthony D. , Roach Daniel E.
Published: December 2006

Silicate minerals grown from glasses, and rapidly cooled melts, often have non-compact branching or ‘spherulitic’ morphology. The branching patterns are observed in volcanic rocks, glasses, meteorites, slags and sometimes in shallow level intrusive rocks. Experiments, observations, theory and simulations all support the concept that the crystal morphology is the result of growth under diffusion limited conditions. We show that in a silicate melt under appropriate conditions the equations for heat transfer and chemical-diffusion reduce to the Laplace equation. This means that the temperature or chemical gradient is a steady state field. Interaction between this field and a random variable (Brownian motion of growth species) is modelled and yields complex branching objects. The growing cluster affects the field such that an in-filled structure cannot be formed. The branching structures of the model crystal are remarkably similar to those formed in nature, and to those produced in laboratory experiments, implying that the model captures the essence of the branching-growth process.
Temperature-dependent disorder in a natural Mg-Al-Fe2+-Fe3+-Spinel
Authors: Della Giusta Antonio , Carbonin Susanna , Ottonello Giulio
Published: December 2006

A natural Mg-Al-Fe spinel from the Balmuccia peridotite (Italian Western Alps) was annealed atTbetween 650 and 1150°C, under controlled oxygen activity, and quenched in H2O. Twenty-three cation distributions were calculated from XRD structural refinements in tandem with microprobe analysis, and verified by Mössbauer spectroscopy in the case of unheated samples.

Unheated crystals showed essentially ordered distribution of Fe3+in octahedral and Fe2+in tetrahedral sites, the only intracrystalline disorder being represented by ∼0.12 atoms per formula unit of[4]Al and[6]Mg. Thermal runs and quenching maintained substantially ordered distribution of Fe2+and Fe3+up to ∼990°C and produced continuous[4]Mg-[6]Al exchange. Between 990 and 1150°C, the previous order of Fe2+-Fe3+appeared to change slightly,[6]Fe2+reaching ∼0.04 afu and[6]Mg ≅[4]Al ≅ 0.24 afu at the highestT. After quenching from this temperature, Fe2+still resided mainly in the T site. Some previously heated crystals underwent reordering on lowering of the temperature.

Experimental data, integrated with existing literature, enabled cation-oxygen distance in this structure to be improved. Results from annealed samples allowed the formulation of an experimental thermometric function based on Mg-Al intracrystalline disorder.
The occurrence of niobian zirconolite, pyrochlore and baddeleyite in the Kovdor carbonatite complex, Kola Peninsula, Russia
Authors: Terry Williams C.
Published: December 2006

The compositions and textural relationships of the oxide minerals zirconolite, pyrochlore and baddeleyite are described. These occur as accessory minerals, often intergrown with each other, from a phoscorite rock associated with the Kovdor carbonatite complex. Both the zirconolite and baddeleyite have relatively high concentrations of Nb and Ta; the pyrochlore is rich in U and Ta. Backscattered electron images, coupled with detailed microprobe analyses, reveal complex compositional zoning in zirconolite and pyrochlore which reflect changes in the fluid composition during growth of these minerals. A comparison is made of incompatible element ratios Zr/Hf, Nb/Ta and Th/U between the three accessory minerals.
A natural ferrous substituted saléeite from Arcu su Linnarbu, Capoterra, Cagliari, Sardinia
Authors: Vochten R. , Van Springel K.
Published: December 2006

Ferrous substituted saléeite is a new variety of saléeite from Arcu su Linnarbu, Sardinia. It is tetragonal with a = 6.982(2) c = 19.660(2) Å, Z = 2; the ideal formula is (Mg,Fe2+)(UO2)2(PO4)2·4H2O. The strongest lines in the X-ray powder diffraction pattern are: 3.473(100)(114), 4.95(50)(110), 4.91(40)(004), 4.443(40)(112), 2.200(30)(118), 2.193(30)(303) and 2.178(30)(009). The mineral is light-yellow in colour and is dull fluorescent. The measured density is 3.242 g/cm3 and Z = 2. There is a prominent (001) cleavage. Refractive indices are : α = 1.572(2) β = 1.577(2) γ = 1.581(2) and 2V = 48°(2). The pleochroism is very weak and the elongation is positive parallel to Y. The mineral occurs as subparallel crystal aggregates with a quadratic outline.
Supra-subduction zone ophiolites of Central Anatolia: geochemical evidence from the Sarikaraman Ophiolite, Aksaray, Turkey
Authors: Yaliniz M. K. , Floyd P. A. , Göncüoğlu M. C.
Published: December 2006

The Central Anatolian Crystalline Complex (CACC), situated between the northern and southern oceanic strands of Neotethys, contain a number of little-studied ophiolitic bodies of late Cretaceous age that have a bearing on the Mesozoic development of this region. The pillow lavas and sheeted dykes of the Sarikaraman Ophiolite were originally a comagmatic differentiated series of vesicular, aphyric and olivine-poor, plagioclase—clinopyroxene phyric tholeiites, but now exhibit greenschist facies assemblages. A set of late dolerite dykes cross-cutting the whole volcanic sequence are more chemically evolved and were probably derived from a different source. Relative to N-MORB the lavas and dykes are enriched in some LIL elements (K, Rb, Cs, U, Th and Sr) and depleted in HFS elements (Nb, Ta, Hf, Zr, Ti and Y) and light REE. In terms of immobile elements the ophiolitic basalts have the broad chemical characteristics of island are tholeiites that were formed in a supra-subduction zone setting, whereas the late dykes are more akin to N-MORB. In this respect the Sarikaraman Ophiolite is similar to other ophiolites found in the eastern Mediterranean region and emphasizes the preservation of this particular environment in the CACC. If all the Central Anatolian Ophiolites (of which the Sarikaraman Ophiolite is one example) were derived via southward thrusting from the Vardar-Izmir-Ankara-Erzincan Ocean branch to the north, age relationships suggest that this segment of ocean crust was relatively short-lived before obduction onto the CACC.
Pyrochlore from Weathered Carbonatite at Lueshe, Zaire
Authors: Wall F. , Williams C. T. , Woolley A. R. , Nasraoui M.
Published: December 2006

A detailed study of weathered pyrochlore in the laterite above carbonatite at Lueshe, NE Zaire, has been made in order to determine its chemical and textural variations. Pyrochlore in fresh carbonatite at Lueshe is close to an ideal formula of (Ca,Na)2Nb2O6(OH,F) (where a general formula is A2−xB2O6(OH,F)1−y·zH2O. The first and principal change on weathering occurs at the base of the profile and involves the leaching and partial exchange of A cations together with hydration. This change appears common to weathered pyrochlore worldwide. As a result weathered pyrochlore at Lueshe has a large apparent A cation deficiency with A totals between 0.25 and 0.59. The B cations remain stable. Abundant kalipyrochlore is unique to Lueshe and is thought to be related to the abundance of potassium feldspar in the fresh carbonatite, showing that the actual composition of weathered pyrochlore is a characteristic of a particular deposit. Weathered profiles at Lueshe are not simple trends from the least to most leached compositions. Further factors including variation in whole rock mineralogy and chemistry, and cation exchange and uptake are responsible for local concentrations of strontio-, bario- and calcium-rich, sodium-poor pyrochlore in the ore body, as well as rims of ceriopyrochlore on kalipyrochlore. The most important textural relationship in the Lueshe pyrochlore is the intimate intergrowth with crandallite in the most weathered parts of the laterite. Although pyrochlore persists throughout the weathering profile, niobium-beating goethite is thought to represent the final product of pyrochlore breakdown.
Monazite-huttonite solid-solutions from the Vico Volcanic Complex, Latium, Italy
Authors: Ventura Giancarlo Della , Mottana Annibale , Parodi Gian Carlo , Raudsepp Mati , Bellatreccia Fabio , Caprilli Enrico , Rossi Paolo , Fiori Salvatore
Published: December 2006

The crystal-chemical relationships occurring within a single grain of monazite-(Ce) from Vetralla, Vico Volcanic Complex, north of Rome, are outlined. The sample is from a miarolitic cavity in a holocrystalline ejectum consisting of K-feldspar plus minor plagioclase, mica and Fe-oxides, collected from a pyroclastic explosive level. The Gandolfi film (Cu-Kα radiation) can be indexed in space group P21/n with a = 6.816(4); b = 6.976(4); c = 6.471(3) Å; β = 103.63(3)°; V = 299.0(6) Å3. Electron-probe microanalyses plot within the field of monazite along the huttonite-monazite edge of the huttonite-monazite-brabantite triangle. Despite patchy and irregular zoning, the grain shows a clear enrichment towards pure monazite at the outer rim. A constant Th:Si ratio of 1:1 indicates the existence of a simple solid-solution between huttonite and monazite. The substitution can be written as Th4+ + Si4+ → REE3+ + P5+ without requiring any electrostatic compensation by divalent cations, or by anionic groups. The REE distribution pattern is compatible with that of monazites from syenitic rocks.
Recognition and significance of multiple fluid inclusion generations in telogenetic calcites
Authors: Muchez Philippe , Slobodnik Marek
Published: December 2006

Ferroan and non-ferroan calcites occur in fractures in the Lower Carboniferous of the Variscan foreland of southern Belgium. These fractures post-date the Variscan orogeny and the calcites have a telogenetic origin. The non-ferroan calcites formed by recrystallization of the ferroan calcites. Two types of monophase aqueous fluid inclusions are present in the ferroan calcite cement. Although both types of inclusions formed at a temperature not exceeding 50°C, one type contains a moderately saline fluid (3.6–16.3 eq. wt.% NaCl) and the other type fresh water (Tm ice = 0°C). The fluid inclusions in the non-ferroan calcite also contain fresh water.

Detailed petrography of the fluid inclusions indicate that the fresh water migrated through the crystals along opened cleavage planes and microfractures. Therefore, they have a secondary origin. The recrystallization of the ferroan calcites to non-ferroan calcites occurred in this fresh water. The saline fluid inclusions are not related to the above mentioned microstructures and although their origin remains unknown, they could represent the ambient fluid from which the ferroan calcites precipitated. The study of the relationship between the occurrence of fluid inclusions and the microstructures seems promising for the identification of fluid inclusions representing post mineral formation fluid and temperature conditions in calcite cements.
Orientation contrast imaging of microstructures in rocks using forescatter detectors in the scanning electron microscope
Authors: Prior David J. , Trimby Patrick W. , Weber Ursula D. , Dingley David J.
Published: December 2006

We have developed a system using ‘forescatter detectors’ for backscattered imaging of specimen surfaces inclined at 50–80° to the incident beam (inclined-scanning) in the SEM. These detectors comprise semiconductor chips placed below the tilted specimen. Forescatter detectors provide an orientation contrast (OC) image to complement quantitative crystallographic data from electron backscatter patterns (EBSP). Specimens were imaged using two detector geometries and these images were compared to those collected with the specimen surface normal to the incident beam (normal-scanning) using conventional backscattered electron detector geometries and also to an automated technique, orientation imaging microscopy (OIM). When normal-scanning, the component of the BSE signal relating to the mean atomic number (z) of the material is an order of magnitude greater than any OC component, making OC imaging in polyphase specimens almost impossible. Images formed in inclined-scanning, using forescatter detectors, have OC and z-contrast signals of similar magnitude, allowing OC imaging in polyphase specimens.

OC imaging is purely qualitative, and by repeatedly imaging the same area using different specimen-beam geometries, we found that a single image picks out less than 60% of the total microstructural information and as many as 6 combined images are required to give the full data set. The OIM technique is limited by the EBSP resolution (1–2°) and subsequently misses a lot of microstructural information. The use of forescatter detectors is the most practical means of imaging OC in tilted specimens, but it is also a powerful tool in its own right for imaging microstructures in polyphase specimens, an essential asset for geological work.
Two new occurrences of benleonardite, a rare silver-tellurium sulphosalt, and a possible new occurrence of cervelleite
Authors: Spry Paul G. , Thieben Scotf E.
Published: December 2006

Benleonardite, ideally Ag8(Sb,As)Te253, occurs in ore specimens from the Mayflower and Gies epithermal gold-silver telluride deposits in Montana commonly spatially associated with hessite and tetrahedrite. In these deposits, it is Cu-bearing (up to 2.7 wt.%) and exhibits a slight deficiency in Ag+Cu coupled with a slight excess in S. A cervelleite-like mineral coexists with benleonardite at Mayflower and is unusual in composition in that it is Se-bearing suggesting the possibility of solid solution with aguilarite (Ag4SeS).
The crystal structure of frankamenite
Authors: Rozhdestvenskaya I. V. , Nikishova L. V. , Lazebnik K. A.
Published: December 2006

Frankamenite, K3Na3Ca5[Si12O30]F3(OH)1H2O, from the Yakutian charoitic rocks, has a triclinic unit cell with the dimensions: a = 10.094(3), b = 12.691(3), c = 7.240(1) Å, α = 90.00(2)°, β = 111.02(2)°, γ = 110.20(2)°, sp.gr. = P1, Z = 1. Its crystal structure has been refined to Raniso= 0.059 (Rw = 0.060) using the intensities of 2563 reflections.

The bases of the structure are zig-zag walls of Ca, Na octahedra joined by infinite octagonal cross-sectioned tubes of SiO4 of the composition (Si12O30). Unlike canasite from the Khibini Mountains, the triclinic cell of frankamenite contains only one silicate tube. The atomic coordinates, interatomic distances and angles are topologically similar to those of canasite. Major differences are observed in the distribution of octahedral cations, which reflect the different anion compositions. Frankamenite exhibits six mixed Ca-Na positions, whereas canasite has only one such position. The H2O molecule is located in the centre of the silicate tube between K+ cations.