bluuebunny/crossref_metadata_2025 huggingface dataset:
The unit-cell of aenigmatite
Authors: Kelsey C. H. , McKie Duncan
Published: December 2006

Redetermination of the unit-cell dimensions as a 10·406 Å, b 10·813 Å, c 8·926 Å, α 104° 56′, β 96° 52′, γ 125° 19′, has shown that the hitherto accepted unit-cell of Gossner and Spielberger (1929) is in error. The morphological unit-cell of Palache (1933) is related to the new unit-cell, to a high degree of precision, by the transformation Palache → Kelsey-MeKie [001∕01½½∕½00]. Fifteen published and two new analyses indicate that the unit-cell contents approach Na+4 [Fe2-10- Ti4+2] Si4+12O2-40. The common twin axis constitutes the diad of a pseudo-monoclinic cell, the (010) plane of which is dimensionally closely related to that of pyroxenes and amphiboles. It is suggested that the aenigmatite structure is based on silicate chains of pyroxene type cross-linked by Ti4+ and Fe2+ on distinct 6-fold sites, with Na+ on sites of higher coordination number. Aenigmatite from volcanic in contrast to that from plutonic parageneses is often submicroscopically twinned and may be inverted from a high temperature monoclinic polymorph.
Microscope accessory plates and colour blindness
Authors: Tocher F. E.
Published: December 2006

The ordinary quartz wedge is adapted for use by the colour blind by the superposition of a two-colour isotropic auxiliary plate. A birefringent plate of suitable retardation may also be used in conjunction with the same auxiliary plate to replace the standard sensitive tint plate. In both cases, diagnostic colour changes are replaced by relative intensity changes.
Theory of Immiscibility in Mineral Systems
Authors: Mueller Robert F.
Published: December 2006

The theoretical basis for the stability of binary and quasi-binary solutions is discussed with special emphasis on miscibility relations. Solutions of the distribution equations are presented for the case of two and three coexisting regular solutions and this model is used to illustrate the energetics of miscibility relations. The same principles are then extended to give a qualitative interpretation to sequences of mineral assemblages consisting of pyroxenes, amphiboles, micas, and feldspars. A formulation is presented for the intrinsic stability of a solution, which depends on the presence or absence of an excess free energy of mixing, and the extrinsic stability of a solution, which depends on the standard free energy of the component end members.
The transformation of groutite (α-MnOOH) into pyrolusite (MnO2)
Authors: Lima-De-Faria J. , Lopes-Vieira A.
Published: December 2006

The transformation of groutite (α-MnOOH) by heating has been studied at 300° C in air, by single-crystal and powder X-ray methods. At this temperature groutite transforms topotactically into pyrolusite (MnO2), the a, b, and c axes of groutite becoming respectively the a, b, and c axes of pyrolusite (in pyrolusite b = a). At various stages of the transformation other weak and diffuse spots were observed on X-ray oscillation photographs, which could not be ascribed to pyrolusite. Some of these extra spots fit well to an α-Mn2O3 structure (isostructural with hematite), with c 14·3 and a 4·9 Å; the other few spots could not be identified.

The transformation of α-MnOOH into MnO2 is explained by a homogeneous mechanism, with migration of protons and electrons to the crystal surface. A detailed interpretation of this mechanism is presented on the basis of the close-packing characteristics of these two structures.
A new universal stage extinction technique: the determination of 2 V when neither optic axis is directly observable
Authors: Tocher F. E.
Published: December 2006

A new universal stage extinction technique is presented. It is based on the special case of coplanar and conical extinction curves where an optic axis lies on the wave-normal locus. It may be used in favourable circumstances to determine 2V when neither optic axis is directly observable.
Four new uranium–lead ages from Cornwall
Authors: Pockley R. P. C.
Published: December 2006

Four new isotopic U/Pb ages from Cornwall are reported. The Pb206/U238 and Pb207/U235 ages for each specimen are concordant. The Pb206/U238 ages are : South Terras mine 225 ± 5 million years (Myr.), Redruth Area 124 ± 4 Myr., Wheal Owles mine 58 ± 3 Myr., and South Terras Area 62 ± 3 Myr. Cell sizes, calculated from X-ray powder photographs, decrease with decreasing ages of the specimens, indicating a progressive increase in the oxidation states of the uranium present. It is concluded tentatively that at least two periods of mineralization affected south-west England at about 290 Myr. and 225 Myr., and that a final event occurred at about 60 Myr. Whether this final event involved the remobilization of older uranium with loss of lead, or the introduction of additional uranium, or a combination of both effects cannot be established from this evidence. No unique explanation has been made for the 124 Myr. age.
Pumpellyite in Snowdonian soils and rocks
Authors: Jenkins D. A. , Ball D. F.
Published: December 2006

Detrital grains, noted during the mineralogical examination of certain Snowdonian soils, have been identified as varieties of the mineral pumpellyite : the source of one variety has been located in dolerites exposed in the area, and the identity of this variety confirmed by X-ray analysis.
The calciferous and alkali amphiboles
Authors: Phillips R. , Layton W.
Published: December 2006

An attempt is made to systematize the nomenclature of the calciferous and alkali amphiboles. The compositions of end-members can be plotted on a simple diagram, which can also be used to display the affinities of the naturally occurring minerals after deriving a basic atomic formula according to the rules given. The composition of an amphibole can in some cases be expressed quantitatively in terms of solid solution of two or three pure end-members.
Polythermal metamorphism of limestones at Kilchoan, Ardnamurchan
Authors: Agrell S. O.
Published: December 2006

Jurassic limestones occurring in a screen between two ring dykes are shown to have undergone two periods of thermal metamorphism; the first characterized by a high ratio of CO2:H2O and the second by a high ratio of H2O:CO2in the vapour phase. The first metamorphism produced minerals characteristic of Bowen's decarbonation series. Some of these minerals became unstable in the second metamorphism and (OH, F) bearing minerals were produced. A stage of fracture-controlled replacement veins with mineral assemblages which indicate a varying CO2:H2O ratio in the vapour and a general falling temperature sequence terminate the metamorphic history. Three new minerals, rustumite (Ca3Si2O7.Caterminate (OH)2), dellaite (Ca12Si6O22(OH)4), and kilchoanite (Ca3Si2O7), of which the last has previously been described, are characteristic of the second episode of metamorphism.
Ultrabasic eruptives with alnöitic-kimberlitic affinities from Malaita, Solomon Islands
Authors: Allen J. B. , Deans T.
Published: December 2006

A detrital assemblage of magnesian ilmenite, pyrope, chrome-diopside, rutile, and zircon has been traced to outcropping ultrabasic alkaline rocks, hitherto unknown in the Melanesian region. Analyses and descriptions of these ‘kimberlite indicator minerals’ are given. The host rocks comprise alnöite, an alnöite breccia with calcite matrix, and a magnesian ankaratrite, which are described, with chemical analyses. Emphasis is laid on the abundance of ultrabasic inclusions and xenocrysts and the replacements and transformations they have undergone. Malaita Island promises to contribute significantly to the understanding of the relations between alnöite, melilite basalts, and kimberlites.
Re-investigation of clino-ferrosilite from Lake Naivasha, Kenya
Authors: Bown M. G.
Published: December 2006

The clino-ferrosilite from the lithophysae in an obsidian from Lake Naivasha, Kenya, originally examined by Bowen (1935), has been shown to be substantially pure FeSiO3, with about 5% MnSiO3 in solid solution. It has the same space-group, P21/c, as clino-enstatite and pigeonite. The unit-cell dimensions are a = 9.718 Å, b = 9·088 Å, c = 5·239 Å, β = 108° 27′. These do not conform to the scheme proposed by Brown (1960): reasons are given why this was not unexpected.
The origin of three garnet isograds in Adirondack gneisses
Authors: Buddington A. F.
Published: December 2006

Three isograds may be drawn, indicating increasing grades of metamorphism in the northern Adirondack area, based on the development of garnet successively in biotite-quartz-plagioclase paragneiss, metadolerite and metagabbro gneiss, and in syenite and quartz syenite orthogneisses. Changes in the accompanying minerals show that this is an order of increasing temperature. Rocks of similar chemical composition, suitable for the development of garnet, occur in each grade of metamorphism and geologic studies indicate adequate temperature and depth for the development of garnet even where it is not present. The degree of development of garnet in rocks of similar chemical composition, in even as high a grade as the pyroxene-granulite subfacies, is widely variable. All of the data are consistent with an hypothesis that the successive development of a garnetiferous facies for each of the different kinds of gneisses mentioned required special conditions that facilitated the kinetics of the reaction, such as temperature in excess of that for equilibria, in order for the garnet reaction to proceed. The data are not conclusive as to whether certain non-garnetiferous facies of amphibolites are due to the physical conditions (such as high partial pressure of H2O for the prevailing temperature and load pressure) or to non-equilibria.
The kyanite isograd in Glen Clova, Angus, Scotland
Authors: Chinner G. A.
Published: December 2006

Mineral data from Glen Clova, Angus, suggest that the development of kyanite in graphite-bearing staurolite mica-schists, treated in terms of a Ca-free system, involved decrease of staurolite and a decrease in biotite MgO:FeO ratio. A kyanite isograd may be defined in Glen Clova as the locality where kyanite joins the assemblage staurolite-garnet-biotite-muscovite-plagioclase-quartz-graphite, the biotite having mol. , although the persistence of this identical assemblage over some 600 metres introduces some uncertainty of interpretation. It is suggested that the reaction staurolite+quartz → garnet+kyanite is unlikely to be a common reaction in nature and that its use to subdivide the amphibolite facies is unjustified.
Sedimentary analcime rocks and sodium-rich gneisses
Authors: Coombs D. S.
Published: December 2006

As indicated by Tilley (1925), albite-rich schists and gneisses can inherit their abnormal chemical characteristics from sediments that are proving to be by no means rare. They may be rich in detrital sodic plagioclase or they may contain authigenie analcime. Some sedimentary analcime rocks (‘analcimolites’) carry normative nepheline and so offer potential parent rocks for nepheline-bearing gneisses provided that, in these gneisses, SiO2 ⩾ (4Na2O+6K2O) in molecular proportions. The chemistry and occurrence of soda-rich sediments are reviewed. Some New Zealand occurrences are newly described and hitherto unpublished analyses are presented for porphyroblastic albite schist and felsitic volcanic arenite from Otago, and for analcime-rich sediments from four localities.
An X-ray powder method for the estimation of (K, Ba) feldspars
Authors: Gay P.
Published: December 2006

Examination of previous physical methods of estimating the barium-content of these feldspars showed that they are generally unsatisfactory. A new variation diagram is constructed correlating BaO content and values of d132 determined from diffractometer records. It is estimated that the BaO content of these feldspars can normally be determined to about 2–3% by using this diagram.

Some of the problems of the mineralogy of the series are reviewed in the light of the experimental results, in particular the effect of polymorphic changes on the variation diagram. Some experimental evidence of the effect of different structural states upon the value of d132 is obtained, and the limitations imposed upon the method by the existence of such states are discussed.
Phase-equilibrium studies in the system NaAlSiO4 (nepheline)–KAlSiO4 (kalsilite)–SiO2-H2O
Authors: Hamilton D. L. , MacKenzie W. S.
Published: December 2006

Phase-equilibrium relations have been determined at 1000 kg/cm2 water pressure for compositions within the system NaAlSi3O8-KalSi3O8-NaAlSiO4-KAlSiO4 in the area adjacent to the temperature minimum. The composition and temperature of the minimum are Ne50Ks19Qz31 and 750° ± 7° C respectively. The compositions of 102 plutonic rocks and 122 extrusive rocks, from Washington's tables, that carry 80% or more of normative Ab + Or + Ne have been plotted; the areas of high density show a marked similarity to the positions of the low-temperature regions of the synthetic system and suggest that many undersaturated rocks are derived by fractional crystallization from a trachytic magma.
Scawtite and its synthesis
Authors: Harker R. I.
Published: December 2006

Since its discovery by Tilley in 1930, scawtite has been recognized in several locations in regions of metamorphosed siliceous limestones. Scawtite is believed to be the same as CSH(A) and, as such, has been synthesized sporadically many times during runs in the CaO-SiO2-H2O system where slight contamination from CO2 has occurred. Attempts to synthesize scawtite were successfully carried out at low partial pressures of CO2 in an excess of water. The stability of selected scawtite compositions lies between 140 and 300° C, and above saturated steam pressures is not pressure-dependent, at least up to 50 000 psi. The scawtite facies (2) lies between the tobermorite-calcite facies (3) and the xonotlite-calcite facies (1). A hydration series exists from (1) to (2) to (3).
A second occurrence of lyndochite
Authors: Horne J. E. T. , Butler J. R.
Published: December 2006

Lyndochite from Tura dukas, 35 miles north of Nanyuki, Kenya, agrees closely with the type material from Canada in its chemical analysis, in the distribution of the rare earths, and in X-ray diffraction data for powder after heat treatment. The mineral is compared and contrasted with aeschynite. Uranium-poor euxenite is intimately associated with lyndochite at the type locality.

Since its discovery over thirty-five years ago, lyndochite has remained unrecorded outside its type locality of Lyndoch Township in Ontario, Canada. Its distinctive chemical composition sets it apart from almost all other Ti-rich metamiet niobates and, despite the many analyses that have been made on rare-earth niobate-tantalates, specimens that could have been regarded as similar to or approximating to lyndochite have rarely been mentioned. Its unusual characteristics include high ThO2 (about 10%) and appreciable rare-earth oxides (about 20%) with a lanthanon assemblage showing a peak concentration of Nd (and Ce), rather than any of the heavy lanthanons. The proportions of TiO2 (about 20%) and (Nb,Ta)2O5 (about 40%) are comparable to those in numerous niobate-tantalates, but are only associated with the percentages of ThO2 and Re2O3 mentioned above in some members of the aesehynite-priorite series. The lyndochite now described is chemically very close indeed to the Canadian lyndochite, and both specimens give closely similar X-ray diffraction patterns (after suitable heat treatment) which are distinct from those of any other metamict mineral.
Weddellite in modern sediments, Florida
Authors: Hutton C. Osborne , Taft William H.
Published: December 2006

Euhedra of weddellite have been recognized in modern, unconsolidated sediments collected from depths of water not exceeding one fathom, along the south-east coast of Florida. For weddellite, the following data have been determined: crystals simple with r {011} accompanied by a {010} in some cases; goniometric axial ratio is a:c = 1:0·593 (meas.), 1:0·5938 (calc.); a0 12·360 Å, c0 = 7·340 Å; space group I4/m, I4 or I4̅; α 1·529, γ = 1·544, δ = 0·015, uniaxial, positive; d22°C = 1·941. Heat treatment of weddellite led to development of whewellite, calcite, and calcium oxide in turn as higher temperatures were employed; fully indexed X-ray diffraction powder data are given for weddellite, in addition to d-spacings and intensities for whewellite.

It is suggested that weddellite developed in the calcareous Florida sediments under conditions of storage over a two-year period, and ahnost certainly was not a constituent of those sediments at the time of collection. This raises the question whether weddellite was present in the Weddell Sea material at the actual time they were recovered by members of the Scotia Expedition.
The significance of the gabbroic xenoliths from Gough Island, South Atlantic
Authors: Le Maitre R. W.
Published: December 2006

The petrography and mineralogy of a series of gabbroic xenoliths, consisting essentially of varying proportions of olivine, clinopyroxene, orthopyroxene, and plagioclase, are described from Gough Island. These are compared with xenoliths from other oceanic localities. Four new analyses of xenoliths and six of pyroxenes are presented, together with some partial analyses of plagioclases. It is concluded that the xenoliths are derived from the mantle above the magma source area. The composition of the mantle in this region is thought to be that of an olivine-tholeiite.
Barringtonite—A new hydrous magnesium carbonate from Barrington Tops, New South Wales, Australia
Authors: Nashar Bebyl
Published: December 2006

Barringtonite, a new hydrous magnesium carbonate of composition MgCO3,2H2O, is recorded from Sempill Creek, Barrington Tops, New South Wales, where it occurs as nodular encrustations on the surface of olivine basalt. The mineral is triclinic, biaxial positive, has refractive indices α = 1·458, β = 1·473, γ = 1·501, 2Vγ = 73° 44′, and using Ito's method (1949) cell dimensions α = 9·155 Å, b = 6·202 Å, c = 6·092Å, α = 94· 00′, β = 95· 32′, and γ = 108° 72′. The three strongest lines on an X-ray powder photograph give d values of 8·682, 3·093, and 2·936 Å.
Basalts from the deep ocean floor
Authors: Nicholls G. D.
Published: December 2006

Basalts dredged from the floor of the deep ocean show general tholeiitic affinities. Some samples are rich in aluminium and of very similar composition to the Warner high-alumina basalt from California. Both olivine tholeiite and high-alumina basalt have been found in the form of glass in dredgings from the Mid-Atlantic Ridge, indicating that liquid magmas of both compositions have been erupted on to the sea bed in this area. In explanation of this association a tentative hypothesis of fractional melting of hydrated upper mantle material is proposed. It is suggested that under the mid-ocean ridges the ‘basaltic fraction’ of the mantle is locally in the form of an amphibole. Fractional incongruent melting of this amphibole appears to be a possible explanation of the range of composition encountered in dredged glass samples.
Noonlcanbahite, a potassic batisite from the lamproites of Western Australia
Authors: Prider Rex T.
Published: December 2006

The coarse-grained wolgidite variety of lamproite from the Wolgidee Hills of the West Kimberley District of Western Australia has previously yielded three new minerals. Two of these, wadeite and magnophorite (Prider, 1939), were discovered and described by the author when working as a research student under Professor Tilley's supervision and the third, priderite (Norrish, 1951), resulted from an X-ray study of material previously considered by the author to be rutile.
Yellow apophyllite from Korsnäs, Finland
Authors: Sahama Th. G.
Published: December 2006

The honey-yellow apophyllite from Korsnäs, Finland, for which chemical, optical, and X-ray data are given, shows a complex twinning. An inner penetration twin is surrounded by two outer penetration twins. The twin laws have been established. The prism faces of the complex crystal are not (100) as conventionally taken for apophyllite but (520). The spacegroup P4/mnc commonly accepted for apophyllite could not be confirmed. It is suggested that the mineral is only pseudotetragonal, the true symmetry possibly being orthorhombic with space group Pnn2 or Pnnm.
The form and internal structure of the alkaline Kangerdlugssuaq intrusion, East Greenland
Authors: Wager L. R.
Published: December 2006

The Kangerdlugssuaq intrusion (68′ 20′ N. 32′30″ W., roughly circular and 33 km across) is of Tertiary age, like the nearby Skaergaard intrusion. At the present level of erosion the outer part is of nordmarkite and inwards there are successive rings of transitional pulaskite (without quartz or nepheline), main pulaskite and, in the centre, foyaite. The different rock types are due to gradual changes in the amounts of certain of the minerals and there are no sharp junctions such as would be expected to result from successive injections.

Zones of inclusions of basalt, fallen from above, dip inwards at 30 to 60° and, in places, there is a platy parallelism of the tabular alkali feldspars dipping similarly inwards. The three-dimensional form of the intrusion is pictured as resembling a pile of saucers of decreasing size, the sequence of formation being from the outer saucer of nordmarkite to the inner, and smaller saucers of increasingly nepheline-rich syenites. Bottom accumulation of crystals is postulated to explain the disposition of the rock types, but the cause of the succession from quartz-bearing to felspathoidal syenites remains uncertain.
Prehnitization in the Yahgan Formation of Navarino Island, southernmost Chile
Authors: Watters W. A.
Published: December 2006

Upper Mesozoic geosynclinal sedimentary rocks, mainly of volcanic (andesitic) derivation, show widespread prehnitization caused by very low grade metamorphism (burial metamorphism). The sediments, which include greywackes, argillites, cherty rocks, and occasional limestone concretions and thin beds, appear little altered in hand specimen and in the field despite the wide extent of recrystalli-zation. Besides prehnite, secondary minerals include quartz, albite, chlorite, sericite, calcite, and sphene. The different modes of occurrence of the prehnite are described and briefly discussed. The alteration of the rocks is compared with similar wide-spread prehnitization recorded in probably correlative rocks on South Georgia.
The thermal disintegration of crocidolite in air and in vacuum
Authors: Patterson J. H.
Published: December 2006

The thermal disintegration of crocidolite has been investigated with X-ray powder and rotation photographs. Initial disintegration products include monoclinic pyroxene, iron oxide phases, and eristobalite as a pseudomorph of the original fibre bundles but at about 1000° C fusion occurs due to incongruent melting of the pyroxene. The products are strongly oriented along the fibre axis and full orientation relationships have been deduced with the aid of structural models. From these relationships it is suggested that regions of the amphibole structure on (100) are retained in the product phases without change in orientation.
A study of uvarovite
Authors: Isaacs T.
Published: December 2006

Uvarovite and its relationships with grossular and andradite have been studied in order to understand better the geochemistry of uvarovite. Synthese have been carried out under both dry and hydrothermal conditions; a solid solution with grossular was obtained under both conditions, but with andradite only under hydrothermal conditions. The results are discussed in relation to the chemistry of uvarovite.
A scheme of cation distribution in the amphiboles
Authors: Ghose Subrata
Published: December 2006

The four principles governing the cation distribution in various octahedral metal sites in the amphibole structure are: Ionic size—the M4 position prefers large cations like Ca2+, Na+; charge balance—when the M4 position is occupied by a monovalent ion, like Na+, Li+, the neighbouring M2 position is occupied by a trivalent ion like Al3+, Fe3+; role of the strongly polarizing cations—cations like Fe2+ prefer the M4 site, since they tend to form covalent bonds with the O4 oxygens; and the role of the (OH) ions—these form part of the brucite layer and repel large or strongly polarizing cations, which tend to distort the regularity of the sheet structure.

The Al-Si distribution in the two different tetrahedral sites are governed by three principles: relief of the Si-O-Si bond strain—Al3+ in the Si1 site causes fewer Si4+ cations to share more than two anions with other Si4+ cations; charge balance—with the introduction of alkali ions in the ‘A’ position, Al3+ is introduced in the Si1 position, since the coordinating oxygens around the A position mostly belong to Si1; and steric considerations—occupation of the M4 site by a large cation tends to rotate the Si2 tetrahedron anticlockwise; Al3+ substitution in the Si1 site rotates the Si1 tetrahedron clockwise and thus the regularity and the constancy of the repeat distance of the silicate double chain is maintained.

Based on these principles, a scheme of cation distribution in the M1, M2, M3, M4, A, Si1, and Si2 positions in the amphibole structure has been derived for most of the common amphibole varieties, except richterite, whose position is anomalous from a crystallochemical point of view.
Alteration products of olivine and pyroxene in basalt lavas from the Isle of Mull
Authors: Fawcett J. J.
Published: December 2006

Flood basalts of the Isle of Mull were sampled in areas outside the metamorphic aureole of the central intrusions. Alteration products of olivine and pyroxene in these rocks are talc, chlorite, serpentine, iron oxides, brucite, calcite, and ‘iddingsite’. Plagioclase feldspar in the same rocks is unaltered. ‘Iddingsite’ is less common than mixtures of chlorite and serpentine.

In two flows the only alteration product near the bottom is ‘iddingsite’ but at higher levels in the same flow green ehloritic material replaces olivine. This variation is accompanied by an increase in the FeO/Fe2O3 ratio in the rock towards the flow top. Green alteration products may be converted to material optically identicaI with ‘iddingsite’ by heating in air at 600° C. Zoned patches of chloritic material have formed by crystallization of the late stage magmatic fluid, modified in composition by reactions with olivine and pyroxene.
Xanthiosite and aerugite
Authors: Davis R. J. , Hey M. H. , Kingsbury A. W. G.
Published: December 2006

Two nickel arsenates from South Terras mine, St. Stephen-in-Brannell, Cornwall, have been shown to be identical with the minerals xanthiosite and aerugite, described by C. Bergemann in 1858, and with two synthetic products described by J. B. Taylor and R. D. Heyding (1958). Xanthiosite is pure golden-yellow, monoclinic, with a 10·174, b 9·548, c 5·766 Å, β 92° 58½′, space group P21/a; with D154=5·42±0·10, the unit cell contains 4[Ni3(AsO4)2] (Dcalc 5·388±0·003). Aerugite is deep blue-green, monoclinic, with a 10·29, b 5·95, c 9·79 Å, β 110° 19′, space-group C2, Cm, or C2/m; the ideal unit cell formula is 2[Ni9As3O16], with one-sixth of the arsenic trivalent; the natural mineral has a lower Ni:As ratio, around 2·6. Both xanthiosite and aerugite are minerals new to Britain.
Mineralogy of certain pyrite concretions from Israel and their alteration products
Authors: Sass E. , Nathan Y. , Nissenbaum A.
Published: December 2006

Pyrite concretions from an arid area of Southern Israel are described. The alteration products include alunite, gypsum, jarosite, baryte, celestine, goethite, hematite, sulphur, and sideronatrite. Sideronatrite is described in detail. The pyrite alteration is considered to be recent and the sideronatrite is preserved owing to climatic aridity. The puzzling appearance of sulphur is tentatively explained by microbiological reduction of the sulphates.
Calciostrontianite in the basal Purbeck beds of Durlston Head, Dorset
Authors: Salter D. L. , West Ian M.
Published: December 2006

A spherulitic mineral occurring as veins and nodules in celestine-bearing secondary limestones in the Lower Purbeck Beds at Durlston Head, Swanage, Dorset, is identified as calciostrontianite, a mineralnot previously recorded from Britain. Textural relationships indicate that it was formed from the alteration of celestine and was in part converted back into celestine. The calciostrontianite originated as an epigenetic mineral during the tectonic movement that gave rise to the Broken Beds.
An occurrence of phlogopite and its transformation to vermiculite by weathering
Authors: Smith Aitken W. W.
Published: December 2006

The characteristics of a phlogopite and its weathering product, vermiculite, have been studied by X-ray, infra-red, electron-microscope, and chemical methods. Inclusions within these minerals have been identified as thin films rich in iron oxide (which impart a schiller effect), spinel (which may exist in a preferred orientation), and serpentine. The orientation relationship between the fresh mica and its weathering product has been established by single-crystal methods. The mechanism of transformation from a 1-layer to a 2-layer polytype is discussed.
An electron-microscope study of peristerite plagioclases
Authors: Fleet S. G. , Ribbe P. H.
Published: December 2006

Plagioclase feldspars in the peristerite range An2-An17 have been investigated by transmission electron-microscopy and electron diffraction. All except the more anorthite-rich specimens were found to be unmixed into albite and oligoclase lamellae, between a few hundred and several thousand Å thick and approximately parallel to . A discussion is given of the part played by these lamellae when optical schiller is exhibited; and the effect of heat treatment on the lamellar structure and optical schiller is described.
Enhanced production of magnesium silicates from strained magnesia
Authors: Bush W. F. , Williamson W. O.
Published: December 2006

Mechanically strained, in contrast to annealed, MgO produced greater yields of forsterite and protoenstatite by solid-state reaction with a quartz–cristobalite mixture at 1200–1400° C. The specific surfaces of the strained and of the annealed MgO were similar. The strained MgO was more hygroscopic and similarity of the surface free energies was thus unlikely. The difference in the amounts of silicates produced from the two types of MgO decreased as the temperatures of synthesis increased. This was ascribed to loss of strain energy by unavoidable annealing before and after these temperatures had been reached.

Similar results were obtained when hydrated silica was substituted for the quartz-eristobalite mixture, but more forsterite was produced.
The crystal structure of sinhalite
Authors: Fang J. H. , Newnham R. E.
Published: December 2006

The Ceylonese gemstone sinhalite, AlMgBO4, is isomorphous with olivine and chrysoberyl. Aluminium and magnesium are oetahedrally coordinated and boron occupies slightly distorted tetrahedra. Because of size differences, the smaller Al ion can be assigned to the inversion symmetry sites, with Mg in mirror plane positions. Least-squares refinement based on single crystal X-ray data gave an accurate set of atomic coordinates with mean interatomic distances: Al-O 1·90, Mg-O 2·10, B-O 1·49 Å.
Italian meteorites
Authors: Baldanza Bartolomeo
Published: December 2006

In an attempt to assemble together the sparse information regarding the eighty meteorites recorded as having fallen in Italy, tables have been prepared dealing respectively with chronology, name and generalities, synonymy, and literature, together with a distribution map. They are intended not only to help correct identification of pieces widespread in museums or private collections, but also to begin a labelling unification process, in order to avoid confusion arising from a wide variety of synonyms.
A meteorite of unique type from Western Australia: The Mount Egerton stony-iron
Authors: McCall G. J. H.
Published: December 2006

A unique meteorite, the existence of which has been known since 1941 but which had been lost, has now been relocated in the form of fragments in two separate collections. Though material available is limited to small fragments, it is sufficient to reveal the principal characteristics of the parent mass, which was a variable body composed of stony material not dissimilar from that of the unbrecciated enstatite-achondrite of Shallowater, Texas, U.S.A., and nickel-iron not dissimilar from the ‘pseudo-octahedrite’ of Horse Creek, Colorado, U.S.A. There is evidence suggesting that it was a stony-iron of a hitherto unrecorded type, and that silicate material predominated.
Pandaite from the Mrima Hill niobium deposit (Kenya)
Authors: Harris P. M.
Published: December 2006

A hydrated barium pyrochlore (pandaite) has been found at Mrima Hill (Kenya) in a residuum consisting mainly of goethite/limonite and gorceixite. The pandaite occurs as pale yellow or white octahedral crystals, which have a micro-crystalline interior. It is isotropic, the refractive index varies from 2·07 to 2·11. The calculated specific gravity is 4·07, and the unit cell dimension is 10·59 Å. After deduction of impurities the following formula was obtained (Na0·03 K0·02 Mg0·05 Ca0·09 Ba0·36 Ln0·05 Th0·01 Pb0·004) (Ti0·21 Nb1·78 Ta0·01) (H2O)1·64 O5·52.

Comparison of the calculated formula, essentially A0·614B2 (H2O)1·64 O5·52 with the ideal pyrochlore formula A2B2O6F indicates important deficiencies in the structure. Differential thermal analysis shows a large endothermic peak at 340° C and moderate exothermic peaks at 480 and 780° C. In its physical, chemical, X-ray, and thermal properties the Mrima pandaite is similar to pandaites described from other localities.

The nature of the alteration of primary pyrochlore to pandaite has been studied using an electron probe.
The thermal decomposition of miscellaneous crocidolites
Authors: Hodgson A. A.
Published: December 2006

Sixteen samples of crocidolite asbestos from weathered zones in mines in Cape Province, Transvaal, Western Australia, and Bolivia have been studied by thermal analysis methods and their characteristics are compared with those of fresh crocidolite from Koegas-Westerberg given by Hodgson, Freeman, and Taylor (1965). New chemical analyses of these samples are reported.

The effect of natural weathering on crocidolite tends to a removal of ¼ of the OH groups and an adjustment of the Fe2+/Fe3+ ratio to unity, but there are only minor changes in the physical characteristics of the fibre. The d.t.a. pattern of decomposition is not affected by weathering, but the endothermic peak corresponding to final decomposition is moved to higher temperatures as the Mg content of crocidolite increases. Mg-blocking of this decomposition is considered to be more important than Mg-blocking of the oxidation reaction at 400–450° C, suggested by Addison et al. (1962).

D.t.a. and other evidence shows that the Transvaal crocidolite contains intergrown amosite fibres, and suggests that the Bolivian crocidolite is admixed with anthophyllite.
The mineralogy of metamorphosed basic rocks from the Willyama Complex, Broken Hill district, New South Wales. Part I. Hornblendes
Authors: Binns R. A.
Published: December 2006

The typical hornblendes of metabasic rocks in the Willyama Complex change from bluish-green to deeply coloured brownish varieties with increase in metamorphic grade. Chemical analyses and optical properties of 23 representative hornblendes are interpreted as showing this colour change to reflect steady increase in titanium content of the hornblendes with increase in grade. High-grade hornblendes also differ from those of lower grade in that tetrahedral aluminium in the Z sites is balanced to an increased extent by alkalis entering the A site rather than by octahedral aluminium entering the Y site. Comparison between theoretical and measured densities of Willyama hornblendes suggest that a calculation based on 23 oxygen anion provides closer approximations than a 24 (O, OH, F) calculation to their structural formulae.
Topotaxy in the system MnO-O-H2O: groutite–ramsdellite–pyrolusite
Authors: Dent Glasser L. S. , Smith Ian B.
Published: December 2006

X-ray and thermal studies in the system MnO-O-H2O show that the transformations groutite(α-MnOOH)-ramsdellite(MnO2)-pyrolusite(MnO2) are topotactic, with the a, b, and c directions of all three corresponding. The reactions proceed by migration of manganese atoms and, where appropriate, protons. Pure single crystals of ramsdellite could not be prepared by heating groutite, even though the two structures are very similar.
Optics of hexagonal pyrrhotine (~Fe9S10)
Authors: von Gehlen Kurt , Pillier Horst
Published: December 2006

Reflectivities of a series of oriented polished sections through a single crystal of pyrrhotine (Fe1−αS) from Trepča, Yugoslavia, were measured by means of a spectral photometer attached to a microscope. This pyrrhotine consists of two phases, namely intermediate pyrrhotine (∼ Fe9S10) and monoclinic pyrrhotine (∼ Fe7S8), which were probably formed by exsolution. The phase relations of pyrrhotine at low temperatures are discussed. Optical data are given for the intermediate pyrrhotine from 440 to 660 mµ. From the reflectivities measured in air and oil against a carborundum standard, values of n, k, and κ were calculated for ω and ε and represented in dispersion curves. Also, sections through the various ‘indicating surfaces’ at 546 mµ are shown. The accuracy of the values, which should be approximately the same for other pyrrhotine phases, is discussed.
Some crystallographic studies in the system CaSOa4-CaSO4.2H2O I. The polymorphism of anhydrous CaSO4
Authors: Gay P.
Published: December 2006

The existence and relationships of the polymorphs of CaSO4have been studied by X-ray methods. Only two distinct phases are found: no crystallographic evidence is available to support the suggestion that theγ-CaSO4structure can have two forms, and it is shown that most previous data on the existence of the high temperatureα-CaSO4polymorphs are likely to be due to decomposition of the sulphate.

Some observations on theγtoβ-CaSO4transformation are reported. The structural implications of these results and their relevance to the nature of the transformation are discussed.
Some crystallographic studies in the system CaSO4–CaSOa4.2H2O II. The hydrous forms
Authors: Gay P.
Published: December 2006

The existence and relationships of hydrated forms both to one another and to anhydrous CaSO4have been studied by X-ray methods. Detailed study of the hemi-hydrate reveals its true cell to be monoclinic and does not confirm the previously suggested polymorphism.

Dehydration studies of the dihydrate and hemi-hydrate are reported; cyclic dehydration and hydration of single crystals of the latter show a variable temperature interval between the formation ofγ-CaSO4and the reconstitution of the hemihydrate at approximately constant humidity. An explanation of this behaviour is offered, and the structural implications of the results of the dehydration studies are discussed.
Potash-trachytes and ultra-potassic rocks associated with the carbonatite complex of the Toror Hills, Uganda
Authors: Sutherland D. S.
Published: December 2006

Rocks containing a high percentage of potash feldspar are described for the first time from the Toror Hills in the Karamoja district of eastern Uganda. They include feldspathic fenites, intrusive feldspathic fenite-breccias, potashtrachytes, and orthoclasites. Petrographic data and chemical analyses show the close similarity in composition of these rocks despite their widely differing textures and modes of occurrence. The potash metasomatism associated with the emplacement of carbonatite, and the subsequent mobilization of these feldspathic fenites are compared with similar phenomena observed at other carbonatite centres. The problem of the mechanism of mobilization is discussed.
Tin-containing andradite from Plavno mine in the Krušné Hory Mts., Czechoslovakia
Authors: Dadák V. , Novák F.
Published: December 2006

Stannian andradite occurs with pyroxene and carbonates, with blende and pyrite as accessories in a skarn deposit in the Plavno mine, Krušné Hory Mts., NW. Bohemia. The green crystals are rhombic dodecahedra up to 3 cm in size. Sp. gr. 3·78; n 1·879; a 12·079±0·002 Å. Quantitative chemical and spectrographic analyses are given; the composition is (Ca2·96Mg0·04Mn0·02)3·02 (Si2·95Sn0·04)2·99O12. The content of tin (SnO2 1·07 %) is isomorphously bound in the lattice, and according to crystallochemical calculations the entrance of tin into the garnet lattice is most probably due to substitution of The presence of tin in the andradite shows that this element was already present in the metasomatic solutions during the process of skarnization.
Garnets from the Eilat area, southern Israel
Authors: Nathan Y. , Katz A. , Eyal M.
Published: December 2006

Garnets from twenty-eight pegmatites, schists, and gneisses from the crystalline massif of Eilat have been examined. Refractive index, unit-cell edge, MnO and FeO content were determined in 19 samples. Three chemical analyses are given. The garnets fall into two distinct groups, the pegmatite garnets (spessartine-rich, almandine to spessartine) and metamorphic garnets (nearly pure almandine). Garnets occurring in pegmatite-like granitoid veins cutting through the schists are shown to belong to the second (metamorphic) group. The pegmatite garnets again fall into two groups of different spessartine content.
Feldspars and pryoxenes from the charnockite aeries of Visakhapatnam area, Andhra Pradesh, India
Authors: Murty M. S.
Published: December 2006

A twin-law study of the plagioclase indicated metamorphic origin of the charnockites and volcanic origin of the basic members of the charnockite series. The original volcanic products have been influenced by the later metamorphism, resulting in the various basic members. The twinning in the plagioclase is considered to be primary. The perthite in the charnockite is of orthoclase variety and indicates a higher temperature of formation than the charnockites of other areas containing microcline. The orthopyroxene in the charnockite series is hypersthene and the clinopyroxene is sahlite. Hypersthene is inferred to have formed at the expense of sahlite, hornblende, biotite, and garnet.
Determination of the optic axes and 2V: electronic computation from extinction data
Authors: Joel N.
Published: December 2006

Extinction readings are taken, on a polarizing microscope, for several wave-fronts in a biaxial crystal (more than four wave-fronts are required). With these extinction data, the machine then calculates the directions of the two optic axes and of the three principal axes of the indicatrix, as well as the value of the optic axial angle 2V, using a least-squares successive approximation technique. The programme was written for an IBM 1620 computer.
An improved water cell for the Emmons double-variation procedure
Authors: Tarney J. , Lacy E. D.
Published: December 2006

An improved water cell for the Universal Stage is described for use in the Emmons double-variation procedure. The cell provides an increased heat flow to the mineral grains, and the technique of orientating and retaining the grains in the centre of the field of view is greatly simplified.
The thermal decomposition of amosite
Authors: Hodgson A. A. , Freeman A. G. , Taylor H. F. W.
Published: December 2006

When amosite (fibrous grunerite, Fe5·5Mg1·5Si8O22(OH)2), is heated in argon or nitrogen, physically combined water is lost up to 500–700° C. Above 500° C (static) or 700° C (dynamic), dehydroxylation occurs endothermically, giving a pyroxene as the main product. Under dynamic heating conditions, part of the hydroxyl water is lost as hydrogen, with concurrent oxidation of the iron. At about 1000° C the pyroxene is decomposed to olivine and cristobalite; at about 1100° C melting begins. In oxygen or air, physically combined water is again lost below 500–700° C. At 350–1200° C a sequence of overlapping dehydrogenation, oxygen absorption, and dehydroxylation reactions occurs, which gives rise to a broad exotherm on the d.t.a. curve. The main products (for static heating conditions) are an oxyamphibole at 350–800° C, and a spinel, hematite, a pyroxene, and X-ray amorphous material at 800–1100° C. Silica crystallizes as cristobalite at 1100–1350° C, and as tridymite at 1450° C. Most of the products in either neutral or oxidizing atmospheres are formed topotactically. The mechanisms and rates of the reactions are discussed, and the problem of determining the chemically combined water in amosite and other minerals of similar composition is considered.
Stability and relations of the Al-Fe epidotes
Authors: Strens R. G. J.
Published: December 2006

The various (P, T) stability fields of iron-free zoisite have been deduced for systems containing excess silica and water with Ca : Al ratios ranging from 1 : 2 (anorthite) to 3:2 (grossular). Zoisite is a possible phase in all systems with Ca:Al lower than 3:2, attaining its maximum stability at the zoisite (Ca:Al = 2:3) and prehnite (Ca:Al = 2:2) compositions.

The consequences of varying the Al : Fe ratio are next examined. Zoisite with 4 % pistacite is stable to 525° at 2 kilobars, compared with ∼585° for clinozoisite and 620 to 630° for epidote (Ps35) at the same pressure. Increasing iron content also stabilizes epidote minerals relative to their low-temperature and high-pressure decomposition products.

Examples of natural zoisite-clinozoisite, zoisite-epidote, and clinozoisite-epidote assemblages are described. It is concluded that zoisite-epidote mixtures result from the disproportionation of clinozoisite outside its own stability field, but within those of zoisite and epidote. The assemblage zoisite-clinozoisite is probably not stable, but further evidence is needed on this point. The assemblage clinozoisite-epidote is stable below 550° C, at which temperature the solvus in the Al-Fe series closes.
New material from, and a reconsideration of, the Dalgaranga meteorite and crater, Western Australia
Authors: McCall G. J. H.
Published: December 2006

Two small fragments of unpromising-looking ferruginous material, recovered from inside the Dalgaranga crater, near Mount Magnet, Western Australia, have been sectioned and, while one is largely composed of iron oxides and adds little to the record of this crater, the second fragment is one of the rare, predominantly stony ones reported by Nininger and Huss, and is sufficiently fresh for a thin section to be prepared. As far as is known no thin sections have been described of material from this crater. Microscopic study with transmitted light shows the stony material to be achondritic and to have affinities with the mesosiderites, and, in spite of the low nickel-iron content of this fragment, it seems preferable to regard it as representative of an iron-poor area within a mesosiderite than as true stony meteorite material. Although closely related to the howardites it cannot be classified with any known achondrite type because of the prominent olivine phenocrysts and it bears no resemblance at all to chondritic material. Mineralogical and petrographical details are described and illustrated, and the significance of this new evidence discussed. The origin of the crater is reconsidered.
Plagioclase twins in some mafic gneisses from Broken Hill, Australia
Authors: Vernon R. H.
Published: December 2006

Plagioclase in mafic gneisses from Broken Hill, Australia, contains twins that can be divided into two groups on the basis of shape: firstly, lamellar twins that gradually change thickness across a grain or form lenticular terminations; and secondly, simple and lamellar twins that show angular steps in the twin interface or form abrupt, planar terminations. The former are interpreted as mechanical twins, and the latter as growth twins formed by grain growth in the solid state, arguing largely by analogy with twin shapes in experimentally produced aggregates, particularly metals. The only twin laws observed in lenticular twins are albite and pericline, these being of nearly equal abundance. Stepped twins are much less common than lenticular twins, and in rocks without lenticular twins most of the plagioclase is untwinned. Several twin laws occur among the stepped twins, but the albite law is the most common. Simple twins on the albite and albite-carlsbad laws are prominent.