bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of iron-bearing rutiles in the paragenesis TiO2-Al2O3-P2O5-SiO2
Authors: Putnis A. , Wilson M. M.
Published: December 2006

Hydrothermal ruffles from a suite of rocks at Mount Perry, Queensland, have been studied in thin section, by electron microprobe analysis, and by transmission electron microscopy. The iron-bearing rutiles, while originally singte-phase, are found to exsolve a sequence of iron-rich precipitates on experimental annealing, with hematite being formed as the stable equilibrium precipitate. Experiments at different temperatures and annealing times enable a time-temperature-transformation plot to be drawn for the exsolution process. The kinetics of this process are used to conclude that the rutiles formed below about 450 °C.
Relations between the spectral reflectance and the chemical composition in the magnetite-ulvöspinel series
Authors: Halfen B.
Published: December 2006

Spectral reflectances and chemical compositions of twenty-eight different grains of exsolved titanomagnetite were measured. Relations between reflectance and composition were established by calculating best-fit planes (Kummell, 1879) for the reflectance at 499 and at 617 nm. These were then transformed to expressions from which the contents of Ti and Mg can be estimated. Even though these estimates are not as accurate as microprobe values, the method is still a useful tool in the study of chemical variation in exsolved titanomagnetites.
The identification of sulphide minerals by infra-red spectroscopy
Authors: Soong R. , Farmer V. C.
Published: December 2006

Synopses

The value of infra-red spectra in identifying sulphide minerals has been assessed by surveying the spectra of some forty specimens. Spectra of finely ground samples dispersed in polyethylene discs were obtained in the region 420-90 cm−1 with a resolution of 3–4 cm−1, using a Beckman-RIIC Fourier-Transform Interferometer. Except for minerals whose metallic conductivity obliterated vibrational features, the spectra permitted rapid recognition of sulphide minerals either alone or in mixtures.

Spectra of the following twenty-five pure, or nearly pure specimens are presented: cinnabar, galena, pyrrhotine, alabandine, sphalerite, wurtzite, realgar, orpiment, stibnite, bismuthinite, arsenopyrite, tetrahedrite, pyrargyrite, proustite, enargite, bournonite, boulangerite, jamesonite, and plagionite. Sulphides whose metallic conductivity led to featureless, almost total, absorption of infra-red radiation included chalcosine, troilite, millerite, covelline, bornite, and pyrrhotine: only the spectrum of the last is illustrated as a typical example.

Comparison of the spectra reproduced here with those previously published show a fair measure of agreement, although there are discrepancies. Povarennykh and co-workers, for example, have reported a common sequence of broad absorption bands at 370, 280, and 180 cm−1 for minerals that were found here to exhibit featureless metal-like absorption. The sources of these and other discrepancies are briefly discussed.
The origin of rhythmic layering
Authors: Maaløe Sven
Published: December 2006

Rhythmic layering in the Skaergaard intrusion shows variation in crystal size and in modal proportions of primocrysts with structural height. These changes are ascribed to variations in nucleation rates of primocrysts. The nucleation theory requires that crystallization occurs under supercooled conditions, and that the crystallization of one primocryst phase may change the composition of the magma in such a manner that the nucleation rates of other primocrysts are influenced. Both these constraints appear to have been fulfilled for the Skaergaard intrusion.
Cryptic variation in the Rhum layered intrusion
Authors: Dunham A. C. , Wadsworth W. J.
Published: December 2006

Electron-microprobe analyses of cumulus olivine, chromite, pyroxene, and plagioclase from layered peridotites and allivalites of the Eastern and Western Layered Series of Rhum demonstrate the presence of cryptic variation. Olivine varies from Fo88-78 within individual units, and there are corresponding changes in the Mg/(Mg+Fe2+) ratios in the pyroxenes and chromites. Plagioclase changes are not so dramatic, but the An-content broadly follows the Mg/(Mg+Fe2+) ratio in the other minerals. The most Fe-(and Na-) rich phases do not occur at the top of lithological units, but some way below. The composition trend above them is reversed. The data are interpreted as the result of periodic infilling of a magma chamber, the new magma mixing with the remains of the previous pulse. Each pulse was followed by a period when fractional crystallization produced the layered rocks. New data on Ni in the olivines suggests that the ratio of the volume of initial magma to volume of layered rocks was about four to one, the initial magma being allied to the high-calcium low-alkali tholeiitic basalts of Skye.
The crystal structure of stilpnomelane. Part III: Chemistry and physical properties
Authors: Eggleton R. A. , Chappell B. W.
Published: December 2006

Full chemical analysis, cell dimensions, γ refractive index, density, and infra-red absorption spectrum have been determined for fourteen stilpnomelanes. Coupled with data from previously described material and electron probe analyses of three further samples, the new information shows that γ = 1·616+0·0047 Fe3+ −0·0037 Mg; substitution of Mn for Fe appears to have little effect on γ. For ferrostilpnomelane, D = 2·85−0·011 Mg, for ferristilpnomelane, D = 2·89−0·011 Mg. Cell dimensions clearly distinguish ferro-, ferri-, and man-ganstilpnomelanes; for ferri-stilpnomelane a = 22·03−0·00446 Mg−0·00786 Fe3+ (Å). A convenient approximation to the structural formula using a ⅛ subcell, is K0·6(Mg, Fe2+Fe3+)6Si8Al(O,OH)27 2–4 H2O.
Sampleite from Jingemia Cave, Western Australia
Authors: Bridge P. J. , Pryce M. W. , Clarke R. M. , Costello M. B.
Published: December 2006

Sampleite from Jingemia Cave, Watheroo (30° 16′ S. 116° 00° E.), 190 km north of Perth, Western Australia is derived from the alteration of copper sulphides in contact with guano deposits. Associated minerals are atacamite, weddellite, and gypsum on goethite and manganese-oxide-coated friable quartz rock. Birnessite, halite, dolomite, taranakite, todorokite, apatite, and malachite are also present.

The sampleite occurs as platy spheroidal aggregates to 0·3 mm with D 3·20±0·01, α 1·625 ∥ [010], β and γ 1·674, all ±0·002, α Turquoise Green 41d to Light Blue-Green 39d, β and γ Benzol Green 41 to Venice Green 41b, absorption α < β = γ, 2Vα 5–10°. Chemical analyses are given.

Cu3(PO4)2·3H2O, a corrosion product reported on artifacts, is believed to be sampleite. A further occurrence of sampleite has been recorded from Brookton, 120 km ESE. of Perth. The structurally related mineral lavendulan has been reported from five Western Australian localities.
Glauconite and celadonite: two separate mineral species
Authors: Buckley H. A. , Bevan J. C. , Brown K. M. , Johnson L. R. , Farmer V. C.
Published: December 2006

Analyses of glauconites and celadonites from continental sedimentary rocks and sea-floor basalts using X-ray diffraction, electron probe microanalysis, infra-red spectroscopy, and X-ray fluorescence spectroscopy are reported. The minerals are shown to be distinct species; each an isomorphous replacement series, glauconite having an average half unit cell of K0·85(Fe3+, Al3+)1·34 (Mg2+, Fe2+)0·66(Si3·76Al0·24)O10(OH)2 whereas celadonite approaches the ideal half unit cell of K(Fe3+, Al3+)(Mg2+, Fe2+)Si4O10(OH)2. Considerable Fe3+Alvi interchangeability occurs in the octahedral layer in both minerals and considerable substitution of aluminium in the tetrahedral layer of glauconites results in the more disordered 1Md type of structure compared with the more highly ordered 1M structure of celadonites. Some mixed layer glauconite-smectites and celadonites were also examined and could be distinguished from true glauconites and celadonites by chemical analysis, XRD, and IR techniques. It is proposed that the terms ‘glauconite’ and ‘celadonite’ should be used only for those minerals containing less than 5% interlayering.
Acicular hornblende schists and associated metabasic rocks from North-West Pakistan
Authors: Kempe D. R. C.
Published: December 2006

Synopses

A suite of unusual acicular hornblende schists is found at Warsak (34° 10′ N. 71°C 23′ E.), some 30 km WNW. of Peshawar, North-West Pakistan. The schists occur in association with sill-like masses of amphibolite facies meta-igneous rocks, possibly a metamorphosed gabbroic and doleritic, dioritic, and granitic calc-alkaline series, and intrusions of alkaline granite and microgranite. These rocks lie within Palaeozoic metasediments and all are folded synclinally. The area was first described by Ahmad et al. (1969).

The rocks of the acicular hornblende schist suite (fig. I) consist essentially of large, idioblastic hornblende crystals—comprising some 30–60 % of the rock—in a fine-grained granoblastic matrix of oligoclase feldspar with minor quartz, iron oxide, biotite, and rutile. The boat-shaped, blue-green hornblendes, twinned on {100}, reach 5 mm in length and are often grouped in sprays or clusters; they are sieved with quartz, ilmenite, and patchy calcite. The groundmass also contains patches and veins of calcite, associated with ragged patchy areas of reddish brown, amorphous iron oxide or hydroxide, perhaps introduced hydrothermally. The schists coarsen in grain size outwards through the sill-form, the hornblendes reaching 4 cm, become rich in chlorite and biotite, and grade into the apparently metagabbroic amphibolitic rocks.

The acicular hornblende schists have a generally basaltic composition, while the hornblendes are tschermakitic. An analysed amphibole has 16·5% Al2O3, is slightly zoned with alumina increasing from core to rim, and has the formula:

Three hypotheses of the origin of the rocks were considered; metamorphism of a suite of basic tufts is the most favoured. Origins involving metamorphism of a lamprophyre-appinite suite or of a gabbroic marginal facies are therefore rejected. Texturally the rocks strongly resemble metatuffs (fig. 2) that occur associated with metagreywackes in the Otago schists of New Zealand (Turner, 1933); like many similar Alpine schists they also contain tschermakitic hornblendes. The Warsak tufts could have formed originally, together with the meta-igneous rocks, possibly as lavas, in an inter-plate tectonic environment; the high A1 content of the hornblende, which is typical of many amphiboles from the surrounding alpine environment in North-West Pakistan, and other mineralogical evidence in the region support a highpressure environment for the metamorphism of the rocks to just within the amphibolite facies, at moderate temperatures of approximately 465 °C.
Crystallization history of sector-zoned microcline megacrysts from the Godani Valley pluton, Nigeria
Authors: Vaniman David
Published: December 2006

Sector-zoning is brought out by mineral inclusions (plagioclase, biotite, hornblende, sphene, and apatite) in 2 to 5 cm microcline megacrysts of the Godani Valley pluton, Nigeria. The inclusions are concentrated in the megacryst rims beneath the faces {110} and {20}; the megacryst cores are not sector-zoned. Comparison with other occurrences (Portugal and Czechoslovakia) shows that this type of sector-zoning is not controlled by growth rate. Chemical sector-zoning does not occur in the Godani megacrysts. Growth from magma is proposed, with preference for inclusions on faces at a high angle to the feldspar a-chain. A superficially similar type of sector-zoning occurs in microcline megacrysts of both pluton and wall rock at Papoose Flat, California, suggesting that this feature can be generated either by growth from magma or by replacement.
Tapiolite, its chemistry and cell dimensions
Authors: Clark A. M. , Fejer E. E.
Published: December 2006

Electron-probe analyses and cell dimensions are reported for twenty members of the tapiolite group. The minerals can be placed in ordered and disordered structural groups, the latter with a significantly larger c dimension. The a and c dimensions for both groups are dependent mainly on their titanium contents. The disordered set form part of a discontinuous series through strüverite/ilmenorutile to rutile. The chemical and structural data are incompatible with the existence of ferrotantalite or mossitc as valid species.
Pyroxenes of basic rocks and rodingites from an ophiolite mélange, south-eastern Turkey
Authors: Hall Robert
Published: December 2006

Ophiolitic rocks occur as a tectonic mélange in the Mutki area of the Eastern Taurus Mountains of south-eastern Turkey. They form the upper part of a Tethyan ophiolite-flysch complex, which is thrust southward over sedimentary rocks of the Arabian foreland (Hall, 1976). The tectonic mélange has a matrix of serpentinite and includes blocks of basic volcanics, gabbros, picrites, and rodingites, most of which have suffered metamorphism and metasomatism. The volcanic rocks have been metamorphosed under conditions transitional between the glaucophane-lawsonite schist facies and the greenschist or greenschist-amphibolite transitional facies of Turner (1968). The picrites have escaped any significant metamorphism, while the gabbros have been partially or completely recrystallized under greenschist facies conditions. Both picrites and gabbros have also suffered calcium metasomatism resulting in the alteration of some of the gabbros to rodingites. Pyroxenes from eight separate blocks from the mélange have been analysed by microprobe (fig. 1) to determine if the pyroxene chemistry is consistent with an igneous origin (as suggested by textural evidence) or if there have been changes due to metamorphism and metasomatism.
Garavellite, FeSbBiS4, a new mineral from the Cu-Fe deposit of Valle del Frigido in the Apuane Alps, northern Tuscany, Italy
Authors: Gregorio F. , Lattanzi P. , Tanelli G. , Vurro F.
Published: December 2006

Garavellite occurs in polished sections, as small aggregates, up to 200 µm across, of anhedral crystals, usually in direct contact with tetrahedrite, Sb-rich bismuthinite, chalcopyrite, and siderite. Chemical formula Fe0,80Cu0.02Sb1.13Bi0.78As0.01S4 on the basis of S = 4, or ideally FeSbBiS4.

The mineral has an orthorhombic unit cell with a = 11.439, b = 14.093, c = 3.754 Å, Z = 4; calculated density 5.64 gm/cm3. Important diffraction lines are 14.00 (m) 010, 7.08 (m) 020, 3.62 (vs) 230, 3.49 (m) 040, 3.34 (m) 320, 3.20 (vs) 121, 3.10 (m) 201, 2.98 (s) 240, 2.89 (s) 221, 2.63 (vs) 311, 2.51 (vs) 250, 2.16 (m) 421, 1.677 (m) 312. In reflected light it is grey with a brown-olive tint similar to that of tetrahedrite. Bireftectance is distinct and anisotropism is also strong, from yellowish-green to bluish grey. Vickers hardness (50 g load) 212–22 kg/mm2. Reflectance in air: 470 nm R1 = 33.5−34.7%, R2 = 40.5– 42.8%; 546 nm 32.8–34.7%, 40.2–42.0%; 589 nm 32.6– 33.7%, 39.3–41.0%; 650 nm 32.4–34.6%, 38.4–41.0%.

The mineral and name have been approved before publication by the Commission on New Minerals and Mineral Names, IMA.

Frigidite, the so-called nickel-bearing variety of tetrahedrite found at this locality, is shown to be an intergrowth of tetrahedrite and Ni-bearing minerals.
New data on wittichenite
Authors: Criddle A. J. , Stanley C. J.
Published: December 2006

The wittichenite (BM 1977, 172) discovered in the course of a reflected light study of polished sections from the Seathwaite deposit, Cumbria (described earlier in this journal by Stanley and Criddle), is the first authenticated occurrence of the species in Great Britain; for this reason it was examined in detail and compared with a specimen (BM 1437) from Wittichen, the type locality. Chemical analyses, cell dimensions, visible-spectrum reflectances, quantitative colour values, and VHN's are provided. They are in agreement with previously published data for the species.
The loss of Fe and Na from a basaltic melt during experiments using the wire-loop method
Authors: Corrigan Gay , Gibb Fergus G. F.
Published: December 2006

Losses of Fe and Na from a typical basaltic liquid during experiments using the wire-loop method have been determined for both Pt and Ag40Pd60 alloy wire by electron-microprobe analyses of the quenched glasses. The amount of Fe lost is dependent on the duration of the experiment and is particularly sensitive to the ratio of sample to metal in direct contact with it. Fe losses can be minimized by using the thinnest wire possible in conjunction with the largest amount of sample that will adhere to the wire and, if Ag-Pd wire is used, can be kept below the 1% level even in long experiments. Much more serious in terms of changes in the bulk composition are losses of Na, which appear to be in direct linear proportion to the length of the experiment and in inverse proportion to the mass of the sample. Even when samples in excess of 200 mg are used the Na losses are unlikely to be less than 5% except in experiments of less than a few days' duration or on samples with very low initial Na contents.
Nukundamite, a new mineral, and idaite
Authors: Rice C. M. , Atkin D. , Bowles J. F. W. , Criddle A. J.
Published: December 2006

A new mineral, nukundamite, from a Fijian kuroko deposit is described. It has been referred to as idaite, Cu5FeS6, or Cu5.5xFexS6.5x. Electron-probe analyses gave Cu 56.51, Fe 9.64, and S 33.51, total with traces of Ag and As is 99.79%. Hexagonal with a 3.782, c 11.187 Å, Z = 1. Empirical formula Cu3.37, Fe0.66, S3.97 on the basis of eight atoms. Copper-coloured, metallic lustre, cleavage {0001} perfect. Density (g cm−3) 4.53 (calc), 4.30 (meas). Strongly pleochroic from reddish orange (Ro) to pale grey (Re). Parallel extinction. Very strong anisotropy with pale green-grey rotation colours. Reflectance values and quantitative colour values in air and oil are given. Similarities with the covelline structure are indicated.

An attempt to fully describe idaite from the Ida mine was unsuccessful. The description of the type material therefore remains inadequate.
Chemical mineralogy of the aureole of the Nahant Gabbro at East Point, Nahant, Mass., USA
Authors: Verma P. K.
Published: December 2006

The Lower Cambrian Weymouth Formation at Nahant, Massachusetts, consisting of interbedded pelitic and calcareous rocks, was intruded by the Nahant Gabbro. The predominant metapelitic mineral assemblage of the contact aureole is quartz-muscovite-chlorite-magnetite-ilmenite. The calcareous hornfelses exhibit a varied mineral assemblage, and in some cases the variation can be spatially related to the intrusive. A number of cross-cutting thin mineral veins, many containing prehnite, are characteristically associated with these calcsilicate rocks.

The minerals have been analysed by electron microprobe and this work indicates the presence of a possible solvus in the Fe3+-Al epidote solid solution series. At the physicochemical conditions of the formation of the Nahant hornfelses, the ferric mole fractions of coexisting epidotes are 0.49 and 0.98.

Comparison with experimental work shows that the conditions of the contact metamorphism were T ≃ 500°C, Ptotal ≃ 2 kb, and XCO2 ≃ 0.2. However, the present assemblages are the result of a later low-grade regional metamorphism, the ultimate product of which was prehnite.
The Moine amphibolite suites of central and northern Sutherland, Scotland
Authors: Moorhouse Steven J. , Moorhouse Valerie E.
Published: December 2006

Three groups of amphibolites within the Moine rocks of Sutherland have been analysed for twenty-six elements by XRF analysis. (1) Very rare epidotic hornblende schists within pelite, possibly derived from volcanic ash deposited penecontemporaneously with the pelite (2 analyses). (2) Major and minor bodies of ‘early Moine’ schistose garnetiferous amphibolite intruded early in the deformational sequence (41 analyses). (3) Small bodies of ‘Loch a' Mhòid metadolerite’, intruded later in the deformational sequence (23 analyses). Rare Moine ultrabasites are associated with these metadolerites and probably formed from the same magma as olivine cumulates. These ultrabasites (5 analyses) are chemically distinct from Lewisian ultrabasites (both in the basement sheets within the Moine rocks of Sutherland and in the foreland Lewisian rocks) and from the Glen Urquhart ultrabasic body (3 analyses).

Using variation diagrams it is inferred that chemical variation in these amphibolites is due largely to pyroxene and plagioclase crystallization in the early amphibolites and olivine, pyroxene, and plagioclase crystallization in the Loch a' Mhòid metadolerites and ultrabasites, followed in both cases by high-level fractionation. This has led to high values of incompatible elements in many of the early amphibolites. Although geochemical discrimination diagrams tend to give ambiguous results for many of these rocks, the early amphibolites are shown to be tholeiitic in nature with a chemistry transitional between within-plate and island-arc type basaltic magma. The Loch a' Mhòid metadolerites are mildly alkaline within-plate type basaltic magma.
An explanation of anomalous optical properties of topaz
Authors: Akizuki Mizuhiko , Hampar Martin S. , Zussman Jack
Published: December 2006

A study has been made of topaz crystals showing a sectoral texture related to the growth of the crystal, and showing anomalous optical properties within the sectors. The growth surfaces responsible for the development of most of the sectors have been identified. The fluorine/hydroxyl sites in topaz are symmetrically equivalent in the solid crystal, but at a growth surface this equivalence may be lost, resulting in a reduction in the crystal symmetry and the ordering of fluorine and hydroxyl, the ordering scheme being retained once the crystal has formed. The reduction in symmetry expected to be produced by this ordering is in general agreement with the actual reduction in symmetry indicated by the optical properties. Heating of the topaz to about 950 °C results in the almost complete disappearance of the optical anomalies due to disordering, which may be related to the loss of hydroxyl from the crystal. Anomalous pyro- and piezoelectric phenomena may also be the result of ordering. Published optical and X-ray determinative curves for fluorine in topaz may give erroneous results for ordered topaz.
The iron-rich blueschist facies minerals: I. Deerite
Authors: Muir Wood R.
Published: December 2006

The mineral deerite is restricted in occurrence to blueschist facies meta-ironstones. From the ideal formula of Si12O40(OH)10 there are a limited range of substitutions: Ti and V for Fe3+ and Mn on the Fe2+ site. In the present survey of deerite compositions from the majority of deerite localities the maximum substitutions have been 2Ti and 3Mn in the above formula. There is an at present unexplained anomaly in the totals of a number of the analyses indicating that there may be variations away from the ideal formula towards increased hydroxyl and decreased cation contents.

From differences between the mineral compatibilities of deerites from the higher-grade Franciscan exotic block blueschist localities and those from more conformable Alpine blueschists, in conjunction with previous work on the experimental stabilities of the low-pressure/low-temperature hydrous iron silicate minerals, it has been possible to map the form of the low-pressure deerite stability field involving reactions of greenalite or minnesotaite or grunerite with magnetite and quartz. Within the deerite stability field, further deerite-forming reactions involve the breakdown of riebeckite and the hydrous incompatibility of magnetite with quartz; both are very dependent on the activity of sodium. A low-pressure stability to 4 kb at 200 °C and 6 kb at 300 °C are estimated from these low-temperature breakdown reactions. This fits in well with the high-pressure deerite stability determinations of Langer et al. (1977).
Weathering mineral facies in altered granites: The importance of local small-scale equilibria
Authors: Meunier A. , Velde B.
Published: December 2006

Classical clay mineralogy determinations and electron microprobe analyses of weathering minerals developed in altered two-mica granites indicate that the chemical forces that produce new minerals are often constrained to small volumes, frequently on the scale of a mineral grain or contact between two grains in the granite.

Chemical potentials such as pH, alkali and alkaline earth and silica activity in the altering aqueous solutions provoke a destabilization of pre-existing minerals, which recrystallize locally to give a new multimineral product. The chemical composition of the new phases is largely governed by the relative concentrations of the elements present in the former minerals.

Three mineral facies were observed in the weathered granites: initially a sericite-beidellitic type, then a beidellite-kaolinitic type, and finally a last stage kaolinite-oxide facies assemblage. The position of each facies is not restricted to a given depth in the profile but the relative proportions of each facies found in a thin-section size sample change towards the kaolinite-oxide facies.

The global rock chemistry reflects the type facies predominant in each sample. The first two facies are roughly silica conservative while the kaolinite-oxide facies loses silica as well as alkali and alkaline earths.

Geochemical and clay mineral studies of rock alteration should consider problems of mineral genesis at very localized sites.
Coexisting sodic and calcic amphiboles from high-pressure metamorphic belts and the stability of barroisitic amphibole
Authors: Ernst W. G.
Published: December 2006

Compositions of glaucophanes and actinolite-hornblende solid solutions occurring in chemically similar metabasaltic rocks from blueschist terranes in east-central Shikoku, W. California, Valtournanche (W. Alps), and W. Liguria are compared. Chemical contrasts among coexisting Na and Ca amphibole pairs, which reflect disparate P-T histories under the presumed attendance of local equilibrium, include: Na contents are rather high among barroisitic hornblendes from the western and Ligurian Alps, as well as among high-grade tectonic blocks from California; in contrast, actinolitic amphiboles from both lower-grade Franciscan tectonic blocks and in situ schists and the blueschists of Shikoku are impoverished in Na relative to blue-green hornblendes. Sodic amphiboles contain less than 0. 5 Aliv per formula unit, whereas Alvi is very high; a situation reversed among calcic amphiboles. The Na + Ca contents ofglaucophanes are strongly clustered around the sum of 2.0 (i.e. A site vacant) whereas calcic amphiboles have a wider range with the A site variably occupied. No solvus has been detected within either sodic or calcic amphiboles under blueschist facies conditions. For low-grade metabasaltic parageneses, a miscibility gap separates these two amphibole groups; at relatively high grade such compositions have sodic calcic amphiboles of barroisitic type; this may mean that glaucophane + hornblende assemblages are metastable, accounting for textural relations indicating that the sodic amphibole typically did not grow at the same time as the barroisite. Ti, Mn, and K appear to be concentrated in calcic amphibole compared to coexisting glaucophane, probably in the M2, M4, and A sites, respectively.

Contrasts in coexisting amphibole tie lines are thought to be a consequence of the fact that the parageneses of Shikoku and California reflect high P and very high P prograde P-T paths respectively, whereas those from Valtournache and W. Liguria show evidence of decompression recrystallization (or back-reaction) of high P (i.e. eclogitic) protoliths. Comparison of the inferred physical conditions operating during the production of these four contrasting paragenetic sequences allows the provisional assignment of a P-T stability region for barroisitic amphibole in metabasaltic rocks as: P 4–5 kb at c. 350°; P 5–7 kb at c. 450 °C.
A Mössbauer spectroscopic study of the cooling history of hypersthene from selected members of the Taupo Pumice formation, New Zealand
Authors: Johnston J. H. , Knedler K. E.
Published: December 2006

57Fe Mössbauer spectroscopy has been used to determine the Mg2+-Fe2+ distribution between the two crystallographically inequivalent cation sites in hypersthenes from a stratigraphic tephra sequence of the Taupo Pumice formation, North Island, New Zealand. From these distributions and X-ray fluorescence analytical data, cooling histories were constructed using previously determined Mg2+-Fe2+ equilibrium isotherms for orthopyroxenes. The results showed that this cooling history geothermometer could be used to enable airfall and airflow tephra to be distinguished. In addition, they showed that the cooling rate of the above deposits correlated better with the deposit thickness, than with the distance of the deposit from the source.
The relationship between euhedral and framboidal pyrite in base-metal sulphide ores
Authors: Ostwald Joseph , England Brian M.
Published: December 2006

Specimens of layered baryte containing a range of pyrite forms, including framboids, framboidal aggregates, spherulites, polyhedra, and zoned euhedral crystals from Kempfield, New South Wales, Australia, have been examined by mineragraphy, X-ray diffraction (XRD), X-ray fluorescence (XRF), and electron-probe microanalysis (EPMA). These investigations showed that the pyrite occurred in two forms—an arsenical variety containing approximately 5% arsenic in solid solution within the pyrite and a non-arsenical variety. EPMA studies indicate that the framboids and the cores of the zoned euhedral crystals have similar levels of arsenic and a genetic relationship is deduced to exist between these forms.
Types of distribution of the minerals of the Meldon Aplite, Devonshire
Authors: Chaudhry M. N. , Mahmood A.
Published: December 2006

Synopsis

A statistical study on the modal analysis data of eight minerals of the Meldon aplite is made with a view to determining their distribution patterns in the rock. Various parameters and statistics have been calculated and the results are tabulated.

Topaz and elbaite are considered as censored samples; ‘normalization’ in the case of these two minerals is obtained by double probit transforms. Findings of the statistical study are correlated with the modes of formation of the minerals.
Motukoreaite—additional data and comparison with related minerals
Authors: Brindley G. W.
Published: December 2006

Motukoreaite resembles hydrotalcite and has positively charged brucite-like layers separated by carbonate and sulphate anions and water molecules. Four phases are recognized. Phase I, the normal mineral with an 11.1 Å basal spacing, readily changes to a mixture of phase I and a partially dehydrated phase II. Phase III with a basal spacing 8.7 Å persists from 50–170°C. Phase II is a pseudo-regular interstratification of phases I and III, with a spacing 11.1 + 8.7 = 19.8 Å; second- and third-order reflections are observed. Phase IV with a 7.5 Å spacing is obtained by treating motukoreaite with sodium carbonate solution to replace SO4 by CO3 anions. Motukoreaite itself shows only slight tendency to transform to a 7.5 Å phase by heat-treatment alone. Comparison is made with the mineral carrboydite, a NiAl sulphate carbonate hydrate. The possibility is considered that sulphate anions may substitute partially in the brucite-like layers to compensate for a deficiency of hydroxyl ions.
Diffuse reflectance spectra and optical properties of some iron and titanium oxides and oxyhydroxides
Authors: Strens R. G. J. , Wood B. J.
Published: December 2006

The reliability and utility of diffuse reflectance spectra are briefly but critically reviewed. The results of measurements of diffuse reflectance over the wavelength range 200 < λ < 2500 nm are reported for wüstite, magnetite, hematite, maghemite, ilmenite, ulvöspinel, and α-FeO · OH (goethite), β-FeO 7sd OH, γ-FeO · OH (lepidocrocite), and δ-FeO · OH. The spectra have been assigned by reference to simplified molecular-orbital energy-level diagrams derived from recent SCF-Xα calculations.

The specular reflectances reported in the Quantitative Data File (Henry, 1977) are related to the diffuse reflectance spectra in a rational way. Minerals that absorb strongly throughout the visible display little dispersion of specular reflectance, and their powders are dark (wüstite, magnetite, ilmenite, ulvöspinel); those that absorb much more strongly in the near ultraviolet than in the visible have specular reflectances that decrease monotonically from blue to red according to a simple dispersion relation derived by combining the Sellmeier dispersion and Fresnel reflexion equations; their powders are strongly coloured (hematite, maghemite, lepidocrocite, goethite) and their optical anisotropy is closely related to crystal structure.
The iron-rich blueschist facies minerals: 2. Howieite
Authors: Wood Robert Muir
Published: December 2006

The mineral howieite has a stability range that extends down to pressures at, or even below, those normally considered to represent blueschist facies metamorphism. Its structure, lying somewhere between a chain and a sheet silicate, can accommodate almost complete iron for manganese substitution as well as the more extraordinary ferrous iron for ferric iron substitution, that is tolerated by changes in the hydroxyl and water content of the unit cell. The ideal formula is NaM12 Si12(O,OH)44, where M is principally manganese and iron but may include limited amounts of aluminium and magnesium. Four new localities for howieite have been discovered by the author and the howieites from the eight localities that have been analysed here help complete the compositional spectrum. The most curious crystallographic feature of howieite is that although the structure seems capable of considerable chemical variation, it is only those howieites of approximate NaMn3Fe8(AlMg)1Si12(O,OH)44 composition that are well crystallized, often growing to over 10 mm in length.
The origin of a tetrahedral diamond
Authors: Seager A. F.
Published: December 2006

The symmetry of diamond is still disputed, and is usually regarded as 4/m3̄2/m or 4̄3m. The (rare) development of tetrahedral morphology has been cited in favour of the lower symmetry. A tetrahedral crystal of c. 4 mm edge-length was studied for evidence relevant to this controversy. Three similar quadrants have nearly plane tetrahedron faces, each surrounded by six curved surfaces belonging to forms {hkl}. The fourth (unique) quadrant, containing (IĪĪ), differs topographically. In the three similar quadrants the tetrahedron faces exhibit coplanar banding of trigons parallel to (IĪĪ), and the curved surfaces have striations parallel to it. The banding and striations are interpreted as stratigraphic etching of nitrogen-rich layers parallel to (IĪĪ) in a type I diamond. Slip, and apparently polygonization, occur in the unique quadrant. The three similar {III} faces were formed by cleavage, and the curved surfaces, banding, and striations by subsequent dissolution. It is probable that (IĪĪ) was part of an original octahedral surface, since tetrahedra of diamond are so rare. The tetrahedral morphology does not necessarily indicate that this crystal belongs to class 4̄3m. The doubt cast upon tetrahedral morphology (and the inferred twinning on {100} or about (100>) as evidence in favour of lower symmetry strengthens the case for assigning diamond to class 4/m3̄2/m.
Cobalt-, nickel-, and iron-bearing sulpharsenides from the north of England
Authors: Ixer R. A. , Stanley C. J. , Vaughan D. J.
Published: December 2006

Within the Alston Orefield of the North Pennines, glaucodot and gersdorffite have been found in samples from Tynebottom Mine, Garrigill, and zoned gersdorffite has been found from Nenthead and the Great Sulphur Vein. At Scar Crag in the English Lake District, glaucodot and alloclase (the first reported occurrence in the United Kingdom) occur associated with arsenopyrite and minor cobaltite and skutterudite. The mineralogy and parageneses of these associations have been studied by ore microscopy, X-ray powder photography, and electron probe microanalysis.

Electron probe microanalysis shows a considerable range in nickel content in the sulpharsenides from the Alston Orefield with a relatively constant Co:Fe ratio. Samples from Scar Crag contain no nickel but exhibit almost a complete range of Co:Fe ratios from FeAsS to CoAsS. The compositions of the Alston Orefield sulpharsenides, in particular, show them to be metastable phases when compared with data from synthetic studies. At Tynebottom Mine, glaucodot and gersdorffite overgrow arsenical marcasite, and at Nenthead and the Great Sulphur Vein, early pyrite framboids or euhedra act as cores to zoned gersdorffite crystals. The Scar Crag sulpharsenides occur in a quartz chlorite apatite vein with the glaucodot and alloclase as overgrowths on arsenopyrite.

In the case of the Scar Crag association, consideration of the compositions of coexisting phases, together with precise determinations of the arsenic content of the arsenopyrites, has permitted speculation regarding temperatures and sulphur activities during ore formation. Estimated ranges are Tc. 400 °C–300 °C and aS2 ≈ 10−9–10−11 11 bar. The occurrence of the sulpharsenides in the Alston Orefield correlates with further geochemical differences compared to other Pennine ores, differences that have been linked to higher temperatures of formation and a magmatic contribution to the ore-forming fluid. The Scar Crag mineralization may be related to a postulated stock intrusion beneath Causey Pike and the geographical proximity of the Alston and Scar Crag occurrences does suggest the possibility of a genetic link.
Nickeloan hydrozincite: a new variety
Authors: Alwan A. K. , Williams P. A.
Published: December 2006

Extensive substitution of Ni for Zn in hydrozincite from the Parc Mine, North Wales, has been observed. This is the first time that a substantial concentration of another transition metal in this mineral has been reported. The average composition of the nickeloan hydrozincite is Zn4.63Ni0.37(CO3)2(OH)6. The relationship of this new variety to other secondary carbonate-containing nickel minerals is discussed, as is the possibility of substitution of other transition metal ions into the hydrozincite lattice.
Irregularities in patterns of element partition
Authors: Henderson Paul
Published: December 2006

In clinopyroxene-melt systems the distribution of chromium and vanadium ions departs from the general pattern of element partition as a function of ionic radius. These departures may be explained by crystal-field effects. Melt structure and the nature of the coordination of cations in the melt also help to determine the pattern of distribution and the extent of the departures from regularity.
Origin of anomalous iron meteorites
Authors: Scott Edward R. D.
Published: December 2006

Anomalous iron meteorites are those which do not have Ni, Ga, and Ge contents appropriate to one of the twelve chemical groups; they account for 14% of all irons. The chemistry of irons in the twelve groups can be largely understood in terms of primary fractionation in the nebula, which established the bulk composition of the groups, and secondary fractionation in the parent bodies (probably fractional crystallization), which produced the chemical trends within groups. Logarithmic element-Ga graphs containing data for groups and anomalous irons reveal that anomalous irons experienced the same primary and secondary fractionations as affected the groups.

The uniformity of chemical trends within groups allows possible genetic relationships between anomalous irons and groups and among anomalous irons to be tested. It is concluded that the sixty-nine anomalous irons are samples from fifty-odd additional groups, which had similar histories to the twelve groups. Less than five of the anomalous irons could be compositional end- members or reprocessed irons from the groups.

Because ‘anomalous’ means abnormal, some other term for the irons which do not belong to the twelve groups would be a useful reminder that these irons formed in a similar way to irons in the major groups. They could be called members of minor groups or grouplets.
Vigezzite, (Ca, Ce) (Nb, Ta,Ti)2O6, a new aeschynite-type mineral from the Alps
Authors: Graeser S. , Schwander H. , Hänni H. , Mattioli V.
Published: December 2006

A new mineral species, vigezzite (Ca,Ce) (Nb,Ta,Ti)2O6, was found near Orcesco, Valle Vigezzo, Prov. Novara, Northern Italy. It forms fiat prismatic crystals up to 2–3 mm length of an orange-yellow colour. The crystals are elongated along the a-axis and flattened on (010). Cleavage at right angles to the prism axis is distinct, fracture conchoidal. Vickers hardness VHN = 396 kp/mm2, corresponding to in the Mohs scale. Refraction indices are high: α = 2.14, γ = 2.315 (NaD, 589 µm), birefringence is 0.175. Optic angle 2Vγ is large. Though intensively yellow coloured, the mineral shows no pleochroism. α = c, β = b, γ = a; optic axial plane is parallel to (010).

Vigezzite is orthorhombie with space group Pmnb or P21nb; a = 7.559±0.01, b = 11.028±0.01, c = 5.360± 0.004 Å, Z = 4. The six strongest lines of the X-ray powder pattern are 4.821 (9) (011), 3.784 (8) (200), 3.036 (10) (031), 2.974 (10) (211), 1.7129 (6) (242), 1.6018 (7) (431).

Electron microprobe analyses lead to the empirical formula (Ca0.82Ce0.24)Σ1.06(Nb0.9Ta0.62Ti0.5)Σ2.02O6. The mineral is not completely homogenous, the ratio Nb/(Nb+Ta) varies from 0.55–0.62. Rynersonite Ca (Ta,Nb)2O6, may represent the Ta-dominant equivalent of vigezzite. Vigezzite occurs together with several other Nb-minerals such as pyrochlore, columbite and fersmite, whose crystallographical and chemical data are reported, in an albitic rock of presumably pegmatitic origin.
The Karroo dolerites of southern Malawi and their regional geochemical implications
Authors: Woolley A. R. , Bevan J. C. , Elliott C. J.
Published: December 2006

The field relationships, petrography and mineralogy, including probe analyses of olivines, pyroxenes, and plagioclases, of the Karroo dolerite dike swarm of southern Malawi, are described. Rock analyses are given and define a typical tholeiitic trend of iron enrichment. The most magnesian rocks are thought to represent fairly picritic liquids. A number of authors have shown that there are significant geochemical differences between the basaltic rocks of the northern and southern parts of the Karroo outcrop in southern Africa, notably for elements such as Al, P, K, Ti, and Ba. The Malawi data presented here, however, show trends that are the reverse of those found hitherto, the Malawi dolerites being closely comparable with the rocks of the central Karroo basin of South Africa and Basutoland. The striking regional variation in the geochemistry of the Karroo basaltic rocks over southern Africa is independent of the tectonics or position vis-à-vis the central Karroo basin, and so probably reflects mantle heterogeneity.
Wolfeite and barbosalite from Thackaringa, Australia
Authors: Plimer I. R. , Blucher I. D.
Published: December 2006

Wolfeite (Fe,Mn)2PO4(OH) and barbosalite FeIIFeIII2(PO4)2(OH)2 are the principal phases in phosphate pods from the core of a zoned altered granitic pegmatite at Thackaringa. Chemical analyses of the wolfeite show it to be Fe-rich and extends the triploiditewolfeite isomorphous series (Frondel, 1949) from ΣFe/Mn = 3·39 (this study) to greater than 100 (Clark and Couper, 1979).
Diffuse reflectance spectra and optical properties of some sulphides and related minerals
Authors: Wood B. J. , Strens R. G. J.
Published: December 2006

The results of measurements of diffuse reflectance over the wavelength range 200 < λ < 2500 nm are reported for sphalerite, cinnabar, alabandite, chalcopyrite, bornite, orpiment, stibnite, bismuthinite, enargite, and pyrargyrite, and for eight pyrite-type and four NiAs-type compounds. Some spectral assignments have been made.

Optical properties are related to the absorption spectrum (and through this to composition and structure) in a rational way. Absolute reflectances tend to increase with mean atomic number (z) through the operation of the ‘z-sum rule’, and at constant z they decrease as the band gap increases. Bireflectance is structurally controlled, being weak in derivatives of the cubic sphalerite and pyrite structures, moderate in derivatives of wurtzite and NiAs, and strong in anisodesmic structures such as that of stibnite. Extreme bireflectance occurs in anisodesmic structures with strong dichroic absorption bands in the visible (molybdenite, covelline).

The dispersion of reflectance (dR/dλ) depends on the position of the centre of the main absorption envelopein relation to the visible spectrum. For λ >, dispersion is normal (Rblue>Rred, dR/dλ negative), the streak is light or coloured, and polished surfaces tend to be bluish. For λ <, dispersion is reversed (Rred>Rblue), the streak is dark, and polished surfaces are yellowish. Polished surfaces are white or grey if absorption varies little through the visible or strongly coloured if it varies rapidly (covelline, chalcopyrite).
Fractures induced by shock in quartz and feldspar
Authors: Lambert P.
Published: December 2006

This study is devoted to fractures produced by natural and artificial shock processes in non-porous rocks consisting essentially of quartz and feldspar. Petrological and textural investigations were performed using optical and scanning electron microscopic techniques. A microfracturation index is adapted from Short (1966, 1968a, b) in order to compare the fracture densities in different materials shocked in different ways. In all cases, the density of fractures in quartz and feldspar increases with increasing pressure to about 200 kb. At higher pressure this trend is reversed. Fracturing is more intense in feldspar than in quartz. Plane shock waves produced in laboratory scale experiments induce more fracturing than natural shock waves. However, such an increase is no larger than the scatter among the data and the experimental technique used in the laboratory can be considered realistic in terms of fracturing. Finally the correlation between pressure and fracture density is too poor to be of use for quantitative pressure calibrations of naturally shocked materials.

There is no direct correlation between the density of fractures and the number of planar elements observed. There is a negative correlation between fracturing and formation of diaplectic glass, Diaplectic glasses are remarkably weakly fractured compared with shocked minerals. The abrupt change in the slope of the curve giving the dependency of the density of fractures with pressure corresponds to the pressure at which diaplectic glass is formed. From petrographic considerations it is deduced that fracturing occurs at the end of the shock sequence, on pressure release, while diaplectic glasses are forming or already formed. Hypotheses of mechanical and thermal fracturing are examined; both are plausible, but a thermal origin may be preferred. The mechanism of formation of diaplectic glass is discussed with respect to results and deductions obtained by the study of fracturing. Diaplectic glass could represent a decompressed highdensity glass resulting from a single state transformation of a mineral, at high pressure.