bluuebunny/crossref_metadata_2025 huggingface dataset:
Amphiboles from the Younger Granites of Nigeria. Part I. Chemical classification
Authors: Borley G. D.
Published: December 2006

The Younger Granites of Nigeria contain varied assemblages of iron-rich ferromagnesian minerals in which amphiboles are an important component. Eighteen of these amphiboles (separated from rocks belonging to nine complexes) have been chemically analysed and the results are presented and discussed. The amphiboles are shown to fall into two groups, a lime-alkali group (comprised of ferrohastingsite of general formula NaCa2Fe″4Fe‴Al2Si6O22(OH)2) and an alkali group (of general formula (Na, K, Ca)2.5–3.0(Fe″, Fe‴)5(Al, Si)3O22(OH)2). The alkali amphiboles are characterized by their extremely low magnesia content, by the presence of Li and F (both in significant amounts), and are of specialinterest because of the unusual amount of ZnO they contain. Optical properties of the amphiboles have been determined but it has not been found possible to use these properties to determine accurately the chemical composition of the alkali amphiboles. It is suggested that, according to current classifications of amphiboles, the analysed alkali amphiboles should be called riebeckitic arfvedsonites or arfvedsonites. The relationship between the hastingsites and the alkali amphiboles is not yet clear.
Amphiboles from the Younger Granites of Nigeria. Part II. X-ray data
Authors: Frost M. T.
Published: December 2006

The cell parameters of fifteen arfvedsonites and four ferrohastingsites were determined using powder and diffractometer techniques and a least squares method of computation. Methods are proposed of distinguishing between calcium- and sodium-rich amphiboles, and between iron-rich and iron-poor varieties of these two groups, by their powder data. Within the arfvedsonite group the b parameter was found to increase with increasing Ca, Fe″, and (OH) and to decrease with increasing Na, F, and Li. The c parameter was found to decrease with increasing F and increase with increasing (Fe‴+Al+Ti). The parameters a, β, and a sin β all tended to increase with increasing Ca, Fe″, and F content. The cell volumes were found to vary with the b parameter. The ferrohastingsites were found to have much larger cell parameters than the arfvedsonites. An attempt was made to explain these variations from structural considerations.
The occurrence of magnesian pyroxenes and magnetite in porphyritic acid glasses
Authors: Carmichael I. S. E.
Published: December 2006

The problem of magnesian pyroxenes in acid liquids is considered in the light of new analyses of pyroxene and magnetite phenocrysts. It is suggested that the early precipitation of titaniferous magnetite, which will strongly deplete the liquid in iron, will decrease the iron:magnesium ratio of the pyroxene components in the liquid. Accordingly the iron:magnesium ratio of a pyroxene precipitating from an acid liquid may vary over a wide range depending upon the presence or amount of early magnetite.
A differential thermal study of the chlorites
Authors: Phillips Wm. Revell
Published: December 2006

Differential thermal analysis alone appears inadequate as a tool for distinguishing the many chlorite varieties; however, this process is capable of yielding much valuable information about the chlorites. The 7 Å septechlorite structure may be easily distinguished from the normal 14 Å chlorite structure. Two stages of dehydration, oxidation of ferrous iron, and structural collapse appear as endothermic and exothermic peaks on the D.T.A. chlorite curves. Septechlorites show only one, large dehydration stage, which leads directly to the structural breakdown. Iron oxidation accompanies the initial dehydration in both structural types, and the temperature at which dehydration begins is noticeably lowered by increasing ferrous iron content of the chlorite variety.
Lamprophyre dykes from Argyll
Authors: Gallagher M. J.
Published: December 2006

In the Carboniferous-Permian dyke-suite north of Loch Sunart, Argyll, a complete gradation is displayed from olivine-dolerite to camptonite. The dolerites are more numerous than the camptonites, and dykes of monchiquite are rare. A small number of minettes and allied lamprophyre types of Devonian age are also present. New analyses of biotite and diopside from a minette and of augite and hornblende from a camptonite are presented, with optical data, and the classification of the dykes briefly discussed.
Simpsonite and stibiotantalite from Benson pegmatite mine, Mtoko, Southern Rhodesia
Authors: von Knorring O. , Hornung G.
Published: December 2006

A new occurrence of the tantalum minerals simpsonite and stibiotantalite is described from a lithium pegmatite at Mtoko, Southern Rhodesia. Optical, chemical, and powder X-ray data are given and the formula of simpsonite is considered; a new formula is proposed.
The Dehydration of Chrysotile in Air and under Hydrothermal Conditions
Authors: Ball M. C. , Taylor H. F. W.
Published: December 2006

Chrysotile fibres, and also single crystals of lizardite, were dehydrated hydrothermally, and the resulting pseudomorphs studied by X-ray rotation photographs. The initial products are normally forsterite and disordered material; talc forms more slowly. At water pressures up to 600 kg/cm2, both forsterite and talc show strong preferred orientation. At higher pressures the talc is oriented but the forsterite tends to be unoriented. The orientation of forsterite formed at 550° C and 500 kg/cm2differs from that found when chrysotile is dehydrated by heating in air. The orientation relationships suggest that, in the dry reaction, the forsterite orientation is controlled mainly by the octahedral layers of the chrysotile, while in the hydrothermal reaction it is controlled mainly by the tetrahedral layers. This does not support the generally accepted mechanism for the dry reaction. New mechanisms are suggested, for both dry and hydrothermal reactions, similar to that already suggested by us for the dehydration of brucite. The formation of talc in the hydrothermal reaction, and of enstatite in the dry reaction above 1000°, are also discussed. The dehydration of talc, to give enstatite, has also been studied using single crystals, and the mechanism of this process is briefly discussed.
Some natural analcime solid solutions
Authors: Wilkinson J. F. G.
Published: December 2006

Chemical, optical, and X-ray data are presented on three analcimes from a differentiation sequence, olivine-theralite to analcime-tinguaite; compared with the ideal analcime composition, they reveal replacement of NaAl→Si. Optical and X-ray data on these minerals accord reasonably well with analcimes possessing similar compositions, and synthesized in the sub-solidus region in the NaAlSiO4-NaAlSi3O8-H2O system.
Note on a chrome and two manganese garnets from India
Authors: Sastri G. G. K.
Published: December 2006

Mineralogic data on a chrome garnet, a spessartine, and a spandite from India are presented. The chrome garnet, named hanléite by Fermor, carries 89·7 % uvarovite, and is not a distinct mineral. The end-member compositions of the manganese garnets, recast from their chemical analyses, lend support to the existence of calderite and blythite as garnet end-members.
Melting relations of Tertiary granitic rocks in Skye and Rhum
Authors: Brown G. M.
Published: December 2006

The results of reconnaissance melting experiments on Tertiary granophyres and Torridonian arkose at 1000 kg/cm2 water-vapour pressure show that the melting behaviour of these rocks can be viewed in relation to the synthetic system NaAlSi3O8-KAlSi3O8-SiO2-H2O. By analogy with this system, P-T curves are constructed for Skye granophyres and, viewed in relation to the stability of tridymite, the depth and temperature of emplacement are estimated. Further estimates of the likely depth of magma generation, and the behaviour of the country rocks at that level, lead to the conclusion that most of the Tertiary granitic rocks were produced through partial melting of Lewisian basement rocks, the heat being provided by the basic magmas available during this volcanic episode. Subsidiary amounts of granitic magma were similarly derived from higher levels, within the Torridonian arkose group, and evidence is provided for the depth and temperature at which these, together with tridymite-bearing metamorphosed arkose in Rhum, were produced.
The högbomite polytypes
Authors: McKie Duncan
Published: December 2006

Single crystal X-ray examination has shown that högbomite forms a series of polytypes, designated nH or nR, with hexagonal or rhombohedral lattices and hexagonal unit-cell dimensions a 5·72 Å, c 4·6 × n Å. The polytypes arise by variation, in a manner as yet undetermined, of the stacking sequence of approximately close-packed oxygen layers with interstitial cations on fourfold and on sixfold sites; the composition of 1/nth of a unit-cell may be represented as R2+1.0_1.6T4+0.2-0.4R3+3.7-4.3O2-7.6-8.0(OH)-0-0.4,, where R2+ = Zn, Fe, Mg, and R2+ = Fe, Al. The polytypes so far observed are 4H, 5H, 6H, 15H, 15R, and 18R. Minerals structurally related to högbomite are nigerite (3H) and taaffeite (4H). A new occurrence of högbomite, polytype 5H, with composition Ti1·7Fe1·6Mg6·3Al18·8Si0·2O40, is described from a spinel-free paragenesis in a magnesian skarn at Mautia Hill, Tanganyika. Another new occurrence in an aluminous xenolith in the Cashel gabbro in Co. Galway, Ireland, is recorded. X-ray powder data are given for two of the polytypes.
The kinetics of the low→high transformation in albite I. Amelia albite under dry conditions
Authors: McKie Duncan , McConnell J. D. C.
Published: December 2006

The transformation was followed in Amelia albite powders by variation in 2θ131−2θ13̄1 with time under isothermal conditions at various temperatures in the range 920°–1080°C. The activation energy of about 74 kcal mole-1 is rather larger than that obtained for the ordering process in synthetic NaAlSi3O8 under hydrothermal conditions.
An unusual distribution of precipitates in a diamond
Authors: Shah C. J. , Lang A. R.
Published: December 2006

The central region of a type 1 stone was found by optical and X-ray topographic examination to be densely populated with small inclusions. The X-ray studies indicated that these were precipitates formed after growth of the stone. Precipitate sizes fell into two groups, 1 µ or less, and around 5 µ. Many cases of decoration of grown-in dislocations by these precipitates were observed.
Some Observations on Igneous Ferrohastingsites
Authors: Borley G. , Frost M. T.
Published: December 2006

Nine ferrohastingsites from the Younger Granites of Northern Nigeria and five from the nepheline-bearing rocks in the Marangudzi complex of Southern Rhodesia have been analysed chemically and their optical properties and unit-cell parameters determined.

All the minerals have compositions that can be expressed by the formula NaCa2(Fe″Mg)4Fe‴Al2Si6O22(OH)2, but the Nigerian minerals differ from those of Marangudzi in their lower alumina contents, generally greater degree of iron enrichment, lower potassium, and more variable fluorine contents. These differences are considered to reflect the differences in composition of their respective parent rocks. The compositional similarities between some hastingsites and barkevikite are commented upon and the pleochroism of barkevikite is briefly discussed.

Refractive indices of the analysed hastingsites have been plotted on the optical curves of Tröger. It is suggested that such curves are of limited use and that variations in unit-cell parameters might be a more useful method of determining the iron contents of hastingsites.

The variation in cell parameters with variation in chemical composition of the analysed minerals is also discussed.
A simple single-axis rotation apparatus
Authors: Hartshorne N. H.
Published: December 2006

The apparatus enables a small crystal to be rotated through 360° about an axis parallel to the stage of a polarizing microscope, while immersed in a liquid of known refractive index. Angles of rotation are measured on a graduated drum to the nearest degree. The working distances separating the crystal from the objective and the condenser are sufficiently small for wide-angle interference figures to be obtained. The crystal is easily mounted and centred.
The stereographic projection: a procedural revision in crystallography
Authors: Oppenheim M. J.
Published: December 2006

Objections are raised to the custom of reversing the pole of projection when dealing with lower crystal faces, for some points so projected no longer retain their natural interangular relations. Instead, lower face normals may be replaced by their antipodal points; these antipodal points are then projected in the usual manner, with suitable symbols. The resultant stereographic projection not only portrays all crystal faces within the primitive circle but is also strictly angle-true.
The recalculation of amphibole analyses
Authors: Phillips R.
Published: December 2006

A good chemical analysis of an amphibole will give cation numbers that can be correlated in detail with the available lattice positions. The substitions that must be recognized are described. A more rigorous check of the analytical results becomes possible and the sources of error may be indicated.
Direct stereographic determination of the optic axes from a ,few extinction measurements: a progressive elimination technique
Authors: Tocher F. E.
Published: December 2006

A new method of determining the optic axes from a few extinction measurements is presented. It is based on the progressive elimination of those parts of the stereogram in which it is obvious that the optic axes cannot lie. It has two applications: as a valid method in its own right, if applied systematically; and as a reconnaissance technique. The second application permits, for example, the recently presented trisogon technique to be rapidly and economically applied over a very small fraction of the stereogram instead of over its whole area.
The spectrochemical determination of feldspars within the field microcline-albite—labradorite
Authors: Fraser W. E. , Downie G.
Published: December 2006

Two spectrochemical methods of feldspar determination are described: one based on the flame spectrophotometer; the other on the quartz spectrograph. For the first method, unknown feldspars are dissolved in a mixture of hydrofluoric and perchloric acids and diluted to 1 : 104. Percentages of Or and An are determined by comparison with dissolved feldspar standards at the same dilution; percentages of Ab are estimated by difference. For the second method, unknown feldspars are burned, unadulterated, in the cathode of the spectrograph arc and a visual estimation is made of the intensities of the following lines: Na5688, Na5683, Ca4455, Ca4435, Ca4425, K4047, K4044, Ca3644, K3447, Na3303, Na3302, and Ca3159. The estimated intensities are then substituted in two empirically determined functions:

(ICa4455+ICa4435+ICa4255+ICa3644+ICa3159)−4/3(INa5688+INa5683+INa3303+INa3302)and (3INa5688+3INa5683+2INa3303+INa3302)−43(4IK4047+3IK4044+2IK3447) .

From the algebraic values of these two functions, the compositions of the unknown feldspars, expressed as percentages of Or, Ab, and An, are read directly from a chart based on results obtained from feldspar standards of known chemical composition.
A zinc phosphate analogue of analcime: kehoeite
Authors: McConnell Duncan
Published: December 2006

Kehoeite, a hydrated zinc aluminate-phosphate, produces an X-ray powder diffraction pattern with interplanar spacings similar to those of analcime, viséite, and pollucite. The diffraction maxima appear to be compatible with a cubic (or pseudocubic) lattice witha13·7 Å. It is concluded that kehoeite is essentially isostructural with analcime and that its framework is composed of linked tetrahedra: (AlO2)−, (H3O2)−, and (PO2)+, as was found to be the case for viséite, which contains (SiO2) in addition. Calculations of the density, the number of oxygens in the unit cell, and the chemical composition are consistent with the structural formula Zn5·5Ca2·5(H2O)32[(Al16P16(H3)16)O96].
Kyanite produced in a granitic aureole
Authors: Lobjoit W. M.
Published: December 2006

An occurrence of kyanite in the inner aureole of a granodiorite intrusion is described from south-western Ghana. Greenschist facies phyllites have been elevated to the amphibolite facies and the regional strike of these country rocks has been disrupted by the intrusion, so that clear evidence is available of the time relationships. It is concluded that the kyanite crystallized as the result of the forceful intrusion of the granodiorite, probably under epizonal conditions.
Some orthopyroxenes from Scottish metamorphic rocks
Authors: Howie R. A.
Published: December 2006

Chemical analyses, cell parameters, and optical properties are presented for seven Scottish orthopyroxenes: four from Harris, two from Scourie, and one from Belhelvie, Aberdeenshire. The compositions range from En83·6 to En55·5. Six of the orthopyroxenes are from pyroxene granulites or related rocks and the other is from a plagioclase-hypersthene hornfels: the latter mineral is notable in having 7·21% Al2O3, causing a considerable contraction in the a and b cell parameters. The alumina content of orthopyroxenes is briefly discussed. Analyses are also given for olivine and diopsidic augite from a South Harris ultrabasic gneiss and for two enderbitic pyroxene gneisses from Scourie.
A hydraulic stage: an aid in counting mineral grains
Authors: Humphries D. W.
Published: December 2006

A hydraulically operated microscope stage is described and constructional details are given. The stage is foot-operated, which leaves both hands free for continuous focusing of the microscope and the operation of a mechanical counting device. A further advantage of the hydraulic stage is that unmounted grains (or small fossils) can be moved smoothly and without relative movement between individual grains. The rate at which grains (or small fossils) can be counted is thus greatly increased.
The oriented transformation of aragonite into calcite
Authors: Dasgupta D. R.
Published: December 2006

The oriented transformation of aragonite to calcite has been studied by X-rays. The [100], [110], and [001] directions of aragonite become [101̄0], [011̄0], and [0001] of calcite. The transformation was completed by a re-orientation of the CO3 groups about the [001] direction of aragonite through an angle of 30°, different rows of CO3 being turned in opposite directions, together with a displacement along the same direction. The layers of Ca ions also are shifted along the basal plane of calcite so that their arrangement perpendicular to the [0001] direction of calcite becomes ABCABCA… instead of ABABABA… as in aragonite.
Arthurite, a new copper—iron arsenate from Cornwall
Authors: Davis R. J. , Hey M. H.
Published: December 2006

Thin apple-green crusts on several specimens from Hingston Down Consols mine, Calstock, Cornwall, proved to consist of a new mineral, alone or intimately mixed with pharmacosiderite (which it closely resembles), or with an unidentified mineral of the alunite-beudantite group having a 7·04, c 16·6 Å, or with both. The new mineral, for which the name arthurite is proposed, for Sir Arthur Russell and Mr. Arthur W. G. Kingsbury, who independently collected material and suggested that it might be new, gives X-ray powder photographs with their three strongest lines at 4·28, 4·81, and 6·97 Å ; the photographs could be satisfactorily indexed on a monoclinic unit-cell with a 10·09, b 9·62, c 5·55o Å (all ± 0·01 Å), β 92·2° ± 0·2° and containing [Cu2Fe4(AsO4)3(OH)7.6H2O]. Chemical analysis on 1·1 mg gave: CuO 16·8, Fe2O3 32·4, As2O5 34·3, H2O 16·5 % (reduced to 100 % after deduction of 27·4 % quartz) ; sp. gr. 3·2 (calc. 3·07). Under the microscope arthurite is pale olive-green and very finely granular; n 1·78, birefringence low to moderate.
The lattice parameters of high-temperature triclinic sodic feldspars
Authors: Carmichael I. S. E. , MacKenzie W. S.
Published: December 2006

The lattice parameters of twenty calcium-bearing anorthoclases and potassium-bearing acid plagioclases have been determined by powder methods. The 201̄ spacing of the homogenized anorthoclases gives a good measure of the Or content irrespective of the amount of calcium present ; this spacing combined with α* (010): (001) may be used to determine the ternary composition of homogeneous feldspars more potassic than approximately Or15. The lattice parameters of feldspars less potassic than Or15 cannot be used for the determination of their ternary composition.
Rhythmic amphibole overgrowths in appinites associated with explosion-breccias in Argyll
Authors: Bowes D. R. , Kinloch E. D. , Wright A. E.
Published: December 2006

Tremolite and actinolite form rhythmic overgrowths over hornblende in appinites associated with pipes of explosion-breccia and represent growth under alternating physical conditions arising from increase of gas pressure and its explosive release. The number of overgrowths present in each appinite mass is related to the number of explosions required to breach the particular structural trap that hindered the upward movement of the volatiles.
Archimedean polyhedra as the basis of tetrahedrally-coordinated frameworks
Authors: Moore Paul B. , Smith Joseph V.
Published: December 2006

The linkage of Archimedean polyhedra has been studied to provide trial models for tetrahedrally-coordinated structures such as zeolites. The cuboctahedron, rhombicuboctahedron, snub cube, icosidodecahedron, rhombicosidodecahedron, and snub dodecahedron cannot be used because four edges meet at a corner. The truncated tetrahedron, truncated cube, and truncated dodecahedron have triangular faces, and are unlikely to occur in silicate frameworks because of the instability of 3-rings. The truncated icosahedron and truncated icosidodecahedron have fivefold symmetry and cannot form four-connected frameworks with lattice symmetry. The truncated octahedron and truncated cuboctahedron may be linked either directly, in combination, or with square, hexagonal, or octagonal prisms. There are nine structures of which four are represented by sodalite, Linde A, faujasite, and ZK-5. The other five have the following properties: truncated octahedra linked H(H-S),Fd3m, a17·5 Å; truncated octahedra linked H′(H-S) and (H-H),P63/mmc, a12·4,c20·5 Å; truncated octahedra linked H′(H-S) and (H-H),P63/mmc, a17·5,c28·5 Å; truncated cuboctahedra linked O′(S-S),Im3m, a15·1 Å; truncated octahedra linked to truncated cuboctahedra H′(S-S),Fm3m, a31·1 Å. The first symbol specifies the linking unit (H hexagon, H′ hexagonal prism, O′ octagonal prism) while the symbols in brackets specify the type of faces opposing across the contact (S square).
Notes on a new occurrence of stilpnomelane from North Wales
Authors: Matthews D. W. , Scoon J. H.
Published: December 2006

An occurrence of stilpnomelane in calcite veins cutting an Ordovician sedimentary iron-ore body has yielded good material for optical and chemical study; data for both ferro- and ferri-stilpnomelane are presented. Associated pyrrhotine, ilmenite, and apatite are briefly described, and a chemical analysis of the apatite shows it to be an extremely pure fluorapatite.
Mboziite, a new sodic amphibole end-member
Authors: Brock P. W. G. , Gellatly D. C. , von Knoebing O.
Published: December 2006

An amphibole occurring in the Mbozi syenite–gabbro complex in SW. Tanganyika approaches very closely to the theoretical end-member Na2Ca;it has α 1·705, pale to light yellow, β 1·713, deep blue-green, γ 1·715, deep blue to green to black, with γ ∥ [010] and β : [001] about 7 to 14°; absorption γ > β ≫ α, with the maximum absorption on (010) at 9 to 12° to [001]. The mineral shows anomalous bright orange-red interference colours and incomplete extinction in sections parallel to (010) even in monochromatic light. X-ray powder data are given. A very similar amphibole occurs in the Darkainle nepheline-syenite complex, Borama district, Somali Republic.
An occurrence of morenosite in Ireland
Authors: King R. J. , Evans A. M.
Published: December 2006

An Irish locality for morenosite is recorded. A chemical analysis shows that a small amount of magnesium is present and this agrees with the composition as indicated by refractive index measurements. X-ray powder data confirm the identification and the genesis of the mineral is briefly discussed.
A numerical system of classification for chlorites and septechlorites
Authors: Phillips W. R.
Published: December 2006

Only two, or at most three, variables can be considered on a two-dimensional composition diagram; six variables must be fixed to completely define a variety of the chlorite or septechlorite groups. The positions of tetrahedral coordination may be described by a single variable and positions of sixfold coordination require three independent variables for complete definition. The number of OH− ions is probably very near the theoretical value of eight, however, it may vary somewhat from this value, and, in so doing, influences the ratio of trivalent and bivalent cations in octahedral coordination.

The normal 14 Å chlorites and 7 Å septechlorites have traditionally been associated together and, although they represent two distinct structural groups, are considered together for classification purposes, since they share many identical variety compositions; a sixth variable denotes structural type, as determined by X-ray powder diffraction or D.T.A.

Each chlorite or septechlorite variety can be described by a numerical notation (chlorite number) consisting of six units and, by dividing the chlorite numbers into units according to accepted nomenclature, each possible chlorite composition can be assigned a variety name, and all variety names can be assigned to a definite composition range.
Layered structure in rocks of the Jotunheim Complex, Norway
Authors: Battey M. H.
Published: December 2006

Two-pyroxene feldspar gneisses and associated ultramafic rocks of the Jotun Kindred in Southern Jotunheimen display mineralogical layering believed to be of original igneous origin. The geological structure of part of the stratiform massif is described, and is shown to provide a basis, hitherto lacking, for systematic study of the mineralogical and chemical variation of the suite.
Hornblendes from some basic hornfelses in the New England region, New South Wales
Authors: Binns R. A.
Published: December 2006

With progressive increase in grade of contact metamorphism, aluminous hornblendes in some New England basic hornfelses change from a pale blue-green variety with ragged actinolitic habit, to a deeper bluish-green variety, then to a deeply coloured brownish type with granular habit. At all stages the coexisting plagioclase is appreciably calcic. No outer aureole of albite-epidote-actinolite hornfels has been recognized. The higher grade hornblendes are richer in alkalis and titanium, and poorer in octahedrally co-ordinated aluminium than those formed at low grades. Two analysed hornblendes display an unusual excess of calcium, which occupies the Y site, and another has a very high content of ferrous iron and potassium.
Trachytes and their feldspar phenocrysts
Authors: Carmicrael I. S. E.
Published: December 2006

The compositions of the groundmass and of the plagioclase and sanidine phenocrysts of a series of over- and under-saturated trachytes indicate that plagioclase will precipitate at some stage in the crystallization interval of all calcium-bearing potassic trachytes. Using this data obtained from natural salic liquids, a concept of crystallization within the system CaA2Si2O8-NaAlSiO4-KAlSiO4-SiO2 may be obtained.
Titania and alumina content of oceanic and circumoceanic basalt
Authors: Chayes Felix
Published: December 2006

Most circumoceanic basalts contain less and most oceanic basalts considerably more than 1·75% of TiO2. The difference of TiO2 averages is large enough to require rejection of the hypothesis that circumoeeanie basalt results from the assimilation of sial by oceanic basalt.
Ages of uraninite and Coffinite from south-west England
Authors: Darnley A. G. , English T. H. , Sprake O. , Preece E. R. , Avery D.
Published: December 2006

The mode of occurrence of uraninite, pitchblende and coffinite at five localities in south-west England is described. Chemical and isotopic analyses of concentrates containing these minerals provide the following 206Pb/238U ages (My.): uraninite, South Crofty, Cornwall, 277 ± 10; uraninite, Geevor, Cornwall, 223 ± 5; pitcbblende-coffinite, King's Wood, Devon, 206 ± 5; pitchblende, Wheal Bray, Cornwall, 165 ± 4; pitchblende, South Terras, Cornwall, 474 ± 2; coffinite, Geevor, Cornwall, c. 45 (chemical analysis only). These results are compatible with geological and mineralogical evidence. Consideration of these and other results indicates that there were at least three periods of uranium mineralization in south-west England, at c. 290 My., c. 225 My., and c. 50 My. Other intermediate ages may also be valid but further work is required to substantiate these.
Clinopyroxenes of the gabbro cumulates of the Kap Edvard Holm complex, east Greenland
Authors: Deer W. A. , Abbott D.
Published: December 2006

The major part of the Kap Edvard Holm complex consists of two series of conspicuously banded gabbroic rocks. The primary minerals of both lower and upper layered series show a progressive change in composition, from higher to lower temperature phases, with increasing height in the complex. Minor fluctuations in the differentiation of the two series occur but the division of the layered rocks into the lower and upper series is based on abrupt and major changes in the compositions of the pyroxenes, olivine and plagioclase. This break is correlated with the injection of a large volume of undifferentiated magma which occurred after much of the lower layered series had consolidated, and from which the rocks of the upper layered series were formed. Twelve pyroxenes, five from the lower and seven from the upper layered series have been analysed; the relationships between their optical properties and chemical composition, and between the cell parameters and composition are considered. The crystallization trend of the pyroxenes is compared with that of the Skaergaard calcium-rich pyroxenes; it is suggested that the restricted enrichment in iron shown by the Kap Edvard Holm pyroxenes may be related to the higher water-vapour pressures which prevailed during much of the period of crystallization.
New petrographical data on the Shiant Isles picrite
Authors: Drever H. I. , Johnston R.
Published: December 2006

A recent bore-hole through the Shiant Isles picrite established the existence of 45 feet more of the picritic facies, and also the lower margin of the silt, at a point almost vertically below the exposed 35 feet previously investigated. In the light of new field and laboratory information the pieritic facies is briefly re-examined and its origin discussed.
Bustamite, rhodonite, spessartine, and tephroite from Meldon, Okehampton, Devonshire
Authors: Howle R. A.
Published: December 2006

Chemical analyses together with optical and physical properties are given for ferroan bustamite, rhodonite, spessartine, spessartine-grossular, and tephroite from contact metamorphosed cale-silicate rocks of the Meldon Railway Quarry, Okehampton. The compositions of these minerals are compared to those from the Treburland manganese mine, Cornwall. An analysis is also given of a spessartine from a pyrrhotite-spessartine skarn rock from the nearby Meldon aplite quarry.
The problem of the potash-rich basaltic rocks
Authors: Joplin Germaine A.
Published: December 2006

It is suggested that the name shoshonite be revived for a group of potash-rich basalts and that the magma from which monzonites, potash-rich syenites, many lamprophyres, nepheline monzonites, shonkinites, eovites, ijolites, leucite basalts, leucitophyres, etc., have crystallized be called the shoshonite magma-type. This series shows parallels with the alkali basalt magma series, and the question of the relation of the two magma-types is discussed.

The name latite is discussed and rejected as a name for this potash-rich magma type. It is further shown that rocks of this composition invade geosynelinal regions that have been recently stabilized, one group of shoshonites being associated with an environment that is still subjected to minor folding and showing some relation to the cale-alkaline rocks, the other a true alkaline suite associated with non-orogenic conditions.
Calculation of the C.I.P.W. norm
Authors: Kelsey C. H.
Published: December 2006

A modification of the rules for the cMeulation of C.I.P.W. norms
when no normative quartz is present is suggested.
The metamorphic facies concept
Authors: Lambert R. St J.
Published: December 2006

Present-day facies schemes are reviewed in relation to their definitions and applicability: a simplification is proposed based on assemblages in basaltic rocks, with secondary facies defined subsequently on pelitic assemblages.
The contamination of a gabbro by Carboniferous Limestone at Carlingford, Co. Louth
Authors: Le Bas M. J.
Published: December 2006

Amongst the layered basic rocks of the Carlingford complex, is a gabbro which has been contaminated by a limited amount of Carboniferous Limestone. The clinopyroxene (Ca49Mg33Fe18) produced in the gabbro is similar to that found in teschenitic gabbros. Such features as the instability of olivine distinguish this contaminated tholeiitic gabbro from true alkaline types. The production of aluminous augite is discussed, and comparison is made with the basic rocks of Scawt Hill and Gunnedah. Analyses of the contaminated gabbro and contained pyroxene are given.
The cathodo-luminescence of minerals in thin section
Authors: Long J. V. P. , Agrell S. O.
Published: December 2006

The cathodo-luminescence of minerals in thin sections of rocks has been examined with the aid of an electron-probe microanalyser and also with a simple electron source producing an unfocused beam. Experimental details of the technique are briefly described and colour photographs, taken at a primary magnification of 30 times, are included. The observed variations in colour and intensity of luminescence are interpreted in the light of electron-probe and spectrochemical determinations of trace elements. Applications of the technique are discussed.
The magnesium aluminium borosilicates: kornerupine and grandidierite
Authors: McKie Duncan
Published: December 2006

A new occurrence of kornerupine in the skarn zone at Mautia Hill, Tanganyika, has yielded unit-cell dimensions a 16·100, b 13·767, c 6·735 Å, density 3·297, and composition Na0·01Mn0·01Ti0·02Mg3·69Fe0·37IIIAl6·36Si3·71B0·41O21·75(OH)0·25. The unit-cell clearly contains 88 anions rather than the 86 proposed previously. Grandidierite from Sakatelo, Madagascar, has unit-cell dimensions a 10·978, b 10·335, c 5·760 Å, space group Pna21 or Pnam, density 2·976, and composition Fe0·12IITi0·01Mg0·88Fe0·03IIIAl3·00Si1·00B0·97O9·00. The unit-cell contains 36 anions and the structure appears to involve A106 chains parallel to the c-axis.
The ‘pseudodiorites’ of Dielette
Authors: Nockolds S. R. , Scoon J. H.
Published: December 2006

An account is given of the mineralogy and chemistry of the ‘pseudodiorites’ of Dielette, the hornfelses from which they are derived, and the contaminated granite veins associated with them.
A test of the discriminant function in the amphibolite problem
Authors: Shaw D. M. , Kudoi A. M.
Published: December 2006

Numerous authors have attempted to use chemical composition as a means of distinguishing amphibolites derived by isochemical metamorphism of basic igneous intrusives or flows from those of sedimentary parentage. In recent years contributions have come from Engel and Engel (1951, 1953, 1962), Lapadu-Hargues (1953, 1958), Poldervaart (1953), Eckelmann and Poldervaart (1957), Wilcox and Poldervaart (1958), Evans and Leake (1960), and Walker, Joplin, Lovering, and Green (1960).
The mineralogy of the British Permian evaporites
Authors: Stewart F. H.
Published: December 2006

The occurrence of the minerals is reviewed. Consideration of their genesis leads to a tentative list of primary minerals, and of early diagenetie, later diagenetic and geothermal metamorphic, and late near-surface changes.
On the chemistry of pillow lavas and the origin of spilites
Authors: Vallance T. G.
Published: December 2006

Twenty-five new analyses of 10 spilitic pillows from the British Isles offer evidence of considerable variability in distribution of components, notably Si, Na, Mg.Fe2+, Ca, Fe3+, and water. Selvedges of pillows have compositions strongly contrasted with but essentially complementary to those of cores. Redistribution of components is believed to have occurred during devitrification. Geosynclinal spilites are regarded as basalts which have suffered such redistribution under conditions of diagenesis or low-grade metamorphism.
The part played by tholeiitic magma in the Carbo-Permian vulcanicity of central Scotland
Authors: Walker Frederick
Published: December 2006

The end-Carboniferous quartz-dolerites form a curious tholeiitic interlude in the alkaline olivine-basalt vulcanicity which characterized central Scotland from the top of the Old Red Sandstone to the Lower Permian. The relationship of the two magma-types is discussed in the light of fresh evidence.
Gyrolite and reyerite from ’S Airde Beinn, northern Mull
Authors: Cann J. R.
Published: December 2006

Reyerite is found in close association with gyrolite in the metamorphic aureole of the volcanic plug of 'S Airde Beinn, northern Mull, and has apparently been formed by metamorphism of the gyrolite. The gyrolite, with a composition close to Ca16Si24O60(OH)3.14H2O, closely approaches trigonal symmetry with a 9·76±0·02 Å and c 3 × 22·26±0·1 Å; biaxial with a small 2V and α 1·537, β 1·547, γ 1·549. The reyerite is trigonal with a 9·76±0·02 Å, c 19·10±0·04 Å and space group Pω 1·568 and ε 1·563, and the unit cell contains about 14 atoms of Ca, 24 of Si (with some substitution by 4(OH)−), and 14H2O as (OH)− and H2O.
The thermal decomposition of crocidolite from Koegas, South Africa
Authors: Hodgson A. A. , Freeman A. G. , Taylor H. F. W.
Published: December 2006

When crocidolite (fibrous riebeckite, Na2Fe3+2Fe2+2·6Mg0·4Si8O22(OH)2 approx.) is heated in argon or nitrogen at 50–400°C, uncombined water is lost. The tensile strength drops sharply at 300–400°C. At 500–600°C under static, or 570–700°C under dynamic conditions, an endothermic dehydroxylation yields an anhydride with a structure close to that of the initial material. At about 800°C, the anhydride decomposes endothermically, giving acmite, cristobalite, a spinel, and liquid. At 950–1000°C the acmite decomposes. Melting is extensive by 1050°C.

On heating crocidolite in oxygen or air, uncombined water is again lost below 400°C. At 300–450°C (static), or 400–600°C (dynamic), hydrogen ions and electrons are lost, to give an oxyamphibole, Na2Fe3+4Fe2+0·6Mg0·4Si8O24. The process is exothermic and probably occurs by proton and electron migration, as suggested by Addison et al. (1962). At 600–950°C the oxyamphibole decomposes endothermically, and most of the remaining Fe2+ is oxidized, giving acmite, hematite, cristobalite, and a spinel. The spinel has largely disappeared by about 950°C, while at 975–1000°C the acmite also decomposes and melting begins.

When crocidolite is heated in hydrogen, no change is detectable by X-rays below 530°C, when the amphibole decomposes to give mainly a pyroxene, metallic iron, cristobalite, and liquid. The same products are detectable up to at least 850°C; the proportion of metallic iron increases with temperature.

With the exception of metallic iron, all the crystalline products formed, whether under neutral, oxidizing, or reducing conditions, show varying degrees of preferred orientation. This could be explained if the reactions occur mainly by the migration of cations through relatively undisturbed oxygen frameworks.
Rhombohedral molybdenite from the Minas da Panasqueira, Beira Baixa, Portugal
Authors: Horrell Clark A.
Published: December 2006

Rhombohedral (3R) molybdenite has hitherto been reported from only one locality. Its mode of occurrence at a new locality is reported in this paper. At Panasqueira it occurs as a rare accessory in greisenized granite with which wolframite-cassiterite-quartz veins are associated. In the veins themselves only normal hexagonal (2H) molybdenite has been detected.
The identification, mode of occurrence, and quantitative determination of crystalline phases in granulated blast-furnace slag
Authors: Steyn J. G. D.
Published: December 2006

This paper describes a technique for the identification and quantitative determination of crystalline phases in granulated blast-furnace slag by means of incident light microscopy on polished and etched samples. The crystalline phases (including periclase) observed in high-magnesia granulates are reported and their mode of occurrence illustrated.
Intergrowths in ilmenite of the beach sands of Kerala
Authors: Rao N. K. , Rao G. V. U.
Published: December 2006

A detailed study of ilmenite concentrates from Chavara and Manaalakurichi deposits has brought to light several interesting textures traceable to exsolution, eutectic crystallization, and replacement and alteration. Magnetite-ilmenite, magnetite-ilmenite-picotite, ilmenite-picotite, ilmenite-hematite, and ilmenite-rutile exhibit exsolution intergrowths. Part of the ilmenite seems to have been formed either by oxidation of ulvöspinel or from a cubic phase of ilmenite by monotropic inversion. Some of the ilmenite-hematite intergrowths display either an emulsoid or a triangular type of texture. Subgraphic intergrowth is observed between ilmenite-magnetite and ilmenite-rutile, suggesting an eutectic relationship between them.

Magnetite-hematite, magnetite-goethite, and magnetite-maghemite intergrowths are the result of alteration of magnetite. Sphene also partly replaces some ilmenite grains.

The proportion of ilmenite grains with and without intergrowths and the probable origin of the intergrowths and their effect on the marketability of ilmenite concentrates are discussed in the paper.
Oriented transformation of manganite during heat treatment
Authors: Dasgupta D. R.
Published: December 2006

The transformation of manganite during heating has been studied by single crystal X-ray diffraction methods. It is observed that manganite transforms into pyrolusite keeping its original axial directions parallel to those of the transformed phase. Pyrolusite then transforms into Mn2O3 with its [001] ‖ [110] or [100] of Mn2O3; of Mn2O3 and [010] ‖ [001] of Mn2O3. Evidence of an intermediate product in the pyrolusite → Mn2O3 reaction has been found.
Mechanism of formation of forsterite and enstatite from serpentine
Authors: Brindley G. W. , Hayami Ryozo
Published: December 2006

Forsterite formed from serpentine powders at various temperatures up to 800° C has been measured quantitatively by X-ray diffraction. The results are considered in relation to a reaction mechanism proposed by Ball and Taylor and are shown to be inconsistent with the details of this mechanism. An alternative mechanism is proposed by which all or nearly all the Mg ions together with some of the Si ions liberated in the reaction zones where water is formed migrate into regions where forsterite is formed. This mechanism is in closer accord with the experimental results. The retarded development of enstatite until temperatures above 1000° C are used is attributed to the nature of the reaction by which it is formed, namely a reaction between forsterite and silica.
The high-temperature behaviour of beryl melts and glasses
Authors: Miller R. P. , Mercer R. A.
Published: December 2006

The course of all crystalline structural changes undergone by the mineral beryl, its melt and glass, has been followed as a function of widely differing but accurately known thermal history. Non-equilibrium ordering processes have been characterized by new techniques in high-temperature microscopy.

The relative influence that beryllium and aluminium ions exert on the phase changes has been established by studies on synthetic melts and glasses representing hypothetical beryls of differing ratios of Be2+:Al3+ ions.

The dynamic changes between the oxide and orthosilicate structures into which the systems reconstitute include the formation of a metastable hybrid beryllium aluminium silicate, which is viewed as a beryllium-containing mullite. The crystallochemical changes have been interpreted in terms of a structural model of the melts and glasses that is shown to be consistent with the ordering effects predicted from the field strengths of the cations.
The mineralogy of the potassium–barium feldspar series
Authors: Roy N. N.
Published: December 2006

Variation diagrams for the optic properties and densities of natural specimens within the series have been determined. They focus attention on two composition regions at about 45 % Cn and 65 % Cn. The significance of the first of these is uncertain, but it is suggested that the discontinuity at 65 % Cn is related to structural changes that take place at this composition.
Mineralogical and radiometric studies of monazite and sphene occurrences in the Namib Desert, South-West Africa
Authors: Burger A. J. , von Knorring O. , Clifford T. N.
Published: December 2006

Monazite and sphene from the central zone of the Damara orogen of South-West Africa, have yielded ages of 500 ± 20 Myr and 600 ± 25 Myr respectively; these results are discussed in relation to the late Precambrian to early Palaeozoic tectono-thermal history of the region. Although chemically similar to that found in carbonatites, the monazite is probably genetically related to the widespread granitic pegmatites that characterize the central zone of the orogen.
The mineralogy of metamorphosed basic rocks from the Willyama Complex, Broken Hill district, New South Wales. Part II. Pyroxenes, garnets, plagioclases, and opaque oxides
Authors: Binns R. A.
Published: December 2006

Chemical and optical data are presented for the orthopyroxenes, clinopyroxenes, garnets, plagioclases, and opaque oxides in high-grade regionally metamorphosed basic rocks and their garnetiferous associates from the Willyama Complex. Exsolution phenomena in the pyroxenes have been studied by X-ray diffraction methods and with the electron probe micro-analyser. The (001) lamellae in one lime-rich clinopyroxene are clinohypersthene. Comparison of the Willyama and other granulite facies clinopyroxenes with those of slowly cooled basic igneous rocks suggests that their chemical compositions may be used as guides to temperature conditions during formation. Willyama plagioclases are complexly twinned and possess intermediate structural states.
Minor element chemistry of leucite and pseudoleucite
Authors: Henderson C. M. B.
Published: December 2006

Leucite and pseudoleucite invariably have lower K/Rb ratios and higher K/Sr and K/Ba ratios than the groundmasses of the rocks in which they occur. The distribution of Rb, Sr, and Ba between K-rich minerals (e.g. alkali feldspars) and the liquids from which they crystallize is generally such that Rb is impoverished and Sr and Ba enriched, relative to K, in the crystallizing phase. Leucite shows the opposite relationship and this is attributed to the leucite structure being sensitive to the size and valency of the ions replacing K.