bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pyroxenes from the early and middle stages of fractionation of the Skaergaard intrusion, East Greenland
Authors: Brown G. M. , Vincent E. A. , Brown P. E. 
Published: December 2006

SummaryCoexisting calcium-rich and calcium-poor pyroxenes have been separated from the gabbros and ferrogabbros of the Skaergaard layered basic intrusion and chemically analysed. Nine new analyses of augites, three of inverted pigeonites, and one of orthopyroxene are presented, together with optical properties. The trend of crystallization of the augites is different from that drawn by previous investigators. The stages at which the orthopyroxene and pigeonite begin and cease to erystallize are defined, and the sub-solidus exsolution and inversion textures of the pigeonites are examined in detail. The characters of the exsolution textures and the degree of pigeonite inversion (monoclinic to orthorhombic pyroxene) are shown to change gradually with height in the intrusion, and are related to a gradual change in the interval between the temperatures of crystallization and inversion.
An investigation of two new minerals: rhodesite and mountainite
Authors: Gard J. A. , Taylor H. F. W. , Chalmers R. A. 
Published: December 2006

SummaryRhodesite, from Kimberley, S. Africa, has been examined by electron-microscope, X-ray, and other methods. The acicular crystals are orthorhombic, with a 23·8, b 6·54, c 7·05 Å.; elongation c, cleavage (100); unit-cell contents approximately (Ca,Na2,K2)8Si16O40.11H2O; optical properties α 1·502, β 1·505, γ 1·515; α = b, β = α, γ = c. With it occurs a similar but distinct fibrous mineral, which appears to be a new species for which the name mountainite is proposed; it is monoclinic, with a 13·51, b 13·10, c 13·51 Å., β 104° elongation b, cleavage (001); unit-cell contents approximately (Ca,Na2,K2)16Si32O80.24H2O; optical properties α 1·504, β 1·510, γ 1·519; β = b (elongation). Both rhodesite and mountainite show close similarities to the fibrous zeolites, mountainite in particular resembling thomsonite. The possible structural basis of these similarities is discussed.
The illite in some Old Red Sandstone soils and sediments
Authors: Mackenzie R. C. 
Published: December 2006

SummaryAn illite separated from an Upper Old Red Sandstone sediment at Denholm Hill Quarry, Roxburghshire, when examined by optical, X-ray, and chemical methods, appeared to be closely similar to Fithian illite. Its composition was , where M+ for the Ca-saturated sample was [(H3O)0·58Ca0·10Na0·06K1·12]. The differential thermal curve showed two peaks: one at 550° C. and the other at 600° C. (i.e. somewhat intermediate between the Fithian and Ballater illites). The dehydration curve was also intermediate. Electron-microscope examination showed rather better crystallization than in Fithian illite. The possible reasons for variation of the illite peak temperature are discussed.
The formation of supergene galena at Broken Hill, Northern Rhodesia (With Plate XXII.)
Authors: Taylor J. H. 
Published: December 2006

SummaryLead-zinc ore-bodies in dolomite at Broken Hill, Northern Rhodesia, consist of a sulphide core surrounded by an oxidized sheath. Oxidation has been proved to persist to a depth of at least 1150 ft. below surface. In the transitional zone between sulphide and oxidized ore galena forms a thin rim to relict masses of blende, and farther into the sulphide core it penetrates the blende along cracks and cleavages. Locally it comprises over 5 % of the ore. From its relations to smithsonite and willemite it is clearly supergene in origin and must have been deposited above the water table. This considerable migration of lead in the zone of weathering is believed to have occurred during a former period of aridity.
Mineralogy of the Silvermines district, County Tipperary, Eire. (With Plates IV to VI.)
Authors: Rhoden H. N. 
Published: December 2006

SummaryThe paragenesis of a suite of hydrothermal minerals (sulphides, baryte, rhombohedral carbonates, quartz, sericite, and chlorite) at four mines in this district is discussed. Of particular interest are the conversion of pyrrhotine to marcasite, which is shown to take place by loss of iron, the replacement of blende by chlorite, and the possible formation of primary goethite. The occurrence of gudmundite is recorded for the first time in the British Isles.
A differentiated boss of alkali dolerite from Cnoc Rhaonastil, Islay. (With Plates Vii and Viii.)
Authors: Walker Frederick , Patterson E. M. 
Published: December 2006

SummaryAn elongated boss of alkali dolerite is described having a NW. trend and measuring 800 m. by 250 m. Two main rock-types occur, an ophitic feldsparrich analeime-olivine-dolerite or leucodolerite and a tesehenite with subhedral pyroxene. The second type is intrusive into the first but the two are associated in vertical veins. Both show local banding and analcime-nepheline-syenite forms a differentiate of both. Finer grained olivine-rich dolerite resembling the crinanites of Jura occurs at the NW. extremity of the boss and probably represents the original magma. All four types have been analysed and are thought to be the products of normal crystal fractionation with slight absolute iron enrichment. The boss was apparently headed not far above the existing exposures and is considered to be of Tertiary age. The pyroxene and olivine of the leucodolerite have been separated and analysed.
X-ray study of psilomelane and cryptomelane
Authors: Mukherjee Bibhuti 
Published: December 2006

SummaryPsilomelane has been shown to be orthorhombic with a 8·254, b 13·40, c 2·864 Å. by the application of Lipson's method. The indexing of powder photographs of psilomelane , where R″ includes the bivalent metals Mn, Ba, Ca, Mg, Co) indicates the space-group P21212 (D22) with one molecule per unit cell. Indexing of powder photographs of psilomelane is not satisfactory with Vaux's axes. Fermor's ‘psilomelane’ is cryptomelane, which is tetragonal with a 9·822, c 2·858 Å. Cryptomelane (KR8O16, where R stands for Mn in different valency states, partly replaced by other cations) is body-centred tetragonal with one molecule per unit cell. Fermor's stalactitic ‘psilomelane’ has an inner dull core of cryptomelane and an outer fine-grained crust of pyrolusite in each needle-shaped body.
A minor occurrence of sepiolite from Puyvalador, near Quérigut, France
Authors: Watters W. A. 
Published: December 2006

SummarySepiolite found as a minor constituent of dolomitie marble bordering tremolite rock from the southern contact zone of the Quérigut granite is briefly described and optical data are presented. A possible paragenesis, following on break-down of the tremolite under the action of carbon dioxide, is suggested.
A method for quantitative mineralogical analysis by X-Ray powder diffraction
Authors: Mitchell W. A. 
Published: December 2006

SummaryA method of quantitative analysis by photometry of X-ray powder diffraction patterns is described. Co-Kα radiation is used and absorption difficulties are overcome by using thin diluted specimens containing an internal standard. An arbitrary universal intensity scale has been established and the values for the stronger lines of a number of minerals are given. Within individual patterns these are consistent with published data obtained by counter diffractometry.
The feldspar phenocrysts of some Tertiary acid glasses
Authors: Carmichael I. S. E. 
Published: December 2006

SummaryThe feldspar phenocrysts of some British and Icelandic Tertiary acid glasses have been studied optically and chemically. Six new analyses of the feldspar phenocrysts are presented together with an anorthoclase from a glassy pantellerite. The analysed feldspars and all the other feldspar phenocrysts that have been examined show high-temperature optics, and confirm the results of previous investigations of plagioclase feldspar determinative curves. The relationship of the feldspar phenoerysts to the plagioclase components in the analysed residual glasses conforms to the synthetic plagioelase system, and the crystallization of feldspar in natural acid melts is considered.
The unique meteorite crater at Dalgaranga, Western Australia
Authors: Nininger H. H. , Huss Glenn I. 
Published: December 2006

SummaryThe first scientific examination of the Dalgaranga crater has revealed specimens exhibiting a variety of structures and compositions hitherto unknown in connexion with any meteorite crater. Excavations have yielded much-weathered specimens and permitted measurements of the form and depth of the original pit. The question of age is considered, and the impacting meteorite is thought to have been largely stony but at least in part a mesosiderite.
Ages of uraninite from two British localities
Authors: Darnley A. G. , Smith G. H. , Chandler T. R. D. , Dance D. F. , Preece E. R. 
Published: December 2006

SummaryUraninite from Geevor Mine, Cornwall, has been analysed by the complete lead method and an age of 290±7 million years has been accepted. Similar studies of uranium from Tyndrum Mine, Perthshire, give an age of 230±8 million years. The significance of the results is briefly considered.
A refinement of the dickite structure and some remarks on polymorphism in kaolin minerals
Authors: Newnham Robert E. 
Published: December 2006

SummaryThe crystal structure of the clay mineral dickite (Al2Si2H4O9) has been refined to a greater accuracy than that reported in an earlier analysis. Improved lattiçe parameters are: a 5·15±0·001, b 8·940±0·001, c 14·424 ± 0·002Å., β 96° 44′± 1′. The dickite structure shows several significant distortions from the geometry of the idealized kaolin layer, including deformation and rotation of the silica tetra-hedra. The most striking features of the octahedral layer are the extremely short shared edges of 2·37 Å. Although the analysis was not sufficiently accurate to position the hydrogen atoms with certainty, a model consistent with the infrared absorption spectra is proposed. The stacking sequences of kaolin-layer minerals have been considered with reference to the structural features observed in dickite. There are thirty-six ways of superposing two kaolin layers commensurate with the OH-O bonds found in kaolinite, dickite, and nacrite. The twelve sequences showing the least amount of cation-cation superposition between consecutive kaolin layers can be used to construct two one-layer cells, kaolinite and its mirror image, and twelve two-layer cells, including dickite and nacrite. The distortions of the kaolin layer introduce secondary variations in the interlayer bonding that suggest that dickite and nacrite are the most stable of the kaolin layer structures, since they possess the shortest oxygen-hydroxyl contacts.
Ages of some uranium and thorium minerals from East and Central Africa
Authors: Darnley A. G. , Horne J. E. T. , Smith G. H. , Chandler T. R. D. , Dance D. F. , Preece E. R. 
Published: December 2006

SummaryThe following ages determined by the complete lead method have been accepted for minerals from a number of localities: uraninite, Nkana, Northern Rhodesia, 522±15 m.y. ; brannerite, Kansanshi, Northern Rhodesia, 503±15 m.y. ; uraninite, Shinkolobwe, Katanga, 642±20 m.y. ; davidite, Mavuzi, Mozambique, 578±15 m.y.; monazite, Monkey Bay, Nyasaland, 597±25 m.y.; samarskite, north-west Kenya, 635±25 m.y. The significance of the results is briefly considered.
Solid-solution relationships in some titaniferous iron oxide ores of basic igneous rocks
Authors: Wright J. B. 
Published: December 2006

SummaryCalculations are presented, based on modal and chemical analyses of titaniferous iron ore minerals from two localities (Skaergaard and Schmoo Lake). They show that Fe: Ti ratios are constant for granular aggregates of ilmenite and titaniferous magnetite formed at any one stage in the cooling history of the containing rock body. From this and other evidence it is concluded that the aggregates are the result of exsolution from original high-temperature cubic solid solutions. For the Skaergaard rocks, the problem of separately crystallized ilmenite, distinct from the granular aggregates, is also discussed.
Metamorphism and metasomatism of rocks of the Moine Series by a dolerite plug in Glenmore, Ardnamurchan (Plate XIX)
Authors: Butler B. C. M. 
Published: December 2006

SummaryA small dolerite plug in Glenmore, Ardnamurchan, has metamorphosed and partially vitrified the adjacent Moine arkoses up to a distance of 6 ft. from the contact. Chemical analyses show that the glasses produced by the metamorphism have compositions close to the ternary minimum in the system NaAlSi3O8-KAlSi3O8-SiO2, indicating that they were formed by fractional fusion of a lowest-melting composition from the arkose. Alkali metasomatism in the metamorphosed arkoses resulted in an increase of Na2O and a decrease of K2O as the contact with the dolerite is approached, while an associated pelitic horizon shows an increase of K2O content. A review of other examples of thermal metamorphism of quartzo-feldspathic rocks by basic intrusions shows that movements of alkalis are very common in this type of environment, and the possible relations of the metasomatism and the fusion are discussed.
An X-ray examination of an exceptionally well crystallized kaolinite
Authors: Goodyear J. , Duffin W. J. 
Published: December 2006

SummarySpecimens of kaolinite have been found in inclusions in the ferruginous deposits on the Yorkshire Coast, just north of Scalby. The excellent quality of the X-ray powder pattern suggests that this kaolinite is better crystalline than kaolinites from other localities. Although the lattice constants of the Scalby material are considered to be identical with those previously published for kaolinite, minor differences in the intensities of the X-ray reflections do occur and may be due to a less distorted structural layer in the Sealby kaolinite.
Beryllium minerals in Cornwall and Devon: helvine, genthelvite, and danalite
Authors: Kingsbury Arthur W. G. 
Published: December 2006

SummaryHelvine and genthelvite are recorded for the first time in Britain; of the former, three occurrences in Cornwall and one in Devon, and of the latter, one occurrence in Cornwall, are described. British danalite has hitherto been represented by two old specimens with the vague locality ‘Redruth’, Cornwall; occurrences at four Cornish localities are described, and a further Cornish locality is provided by two old specimens previously labelled as garnet. Partial chemical analyses for the helvine, genthelvite, and danalite specimens are presented; helvine and genthelvite occur in pyrometasomatic-hydrothermal deposits in metamorphosed calcareous sediments and, in one instance, in greenstone; danalite in hydrothermal deposits or lodes in metamorphosed greenstone; the parageneses of the three minerals are discussed.
Mineral Analysis and Analysts
Authors: Hey M. H. 
Published: December 2006

SummaryThe history of the chemical analysis of minerals is shortly reviewed. Following rapid developments between 1770 and 1810, few important changes took place for close on 130 years; new procedures led to simpler and more convenient separations but not, on the whole, to greater accuracy. The older analyses are, in general, neither worse nor better than modern ones, and analyses can only be assessed on internal evidence, if available, or on the reputation of the analyst.The development of microchemical and colorimetric techniques in the last 40 years has resulted in a great reduction in the amount of material required for a mineral analysis; 5 to 20 mg is usually sufficient, and in favourable cases a complete analysis may be possible on less than I mg. Some modern instrumental methods are considered, and it is concluded that they cannot wholly replace the classical wet-chemical methods in their modern developments.W. F. Hillebrand (1894) deplored the tendency of some petrologists to demand large numbers of very incomplete rock analyses, and his remarks are considered apposite today.
Hematophanite, a derivative of the perovskite structure
Authors: Rouse R. C. 
Published: December 2006

SummaryHematophanite, ideally Pb4Fe3O8Cl, is tetragonal, space group P4mm, with a = 3·92 and c = 15·31 Å. The crystal structure, which has been refined to an R-factor of 9·1 %, may be described as an interlayering of perovskite-like units with a cesium chloride or, alternatively, a nadoritelike unit. The nadorite-like part consists of a double layer of PbO4Cl4 distorted square antiprisms. Iron atoms are in 6-fold (tetragonal bipyramidal) and 5-fold (square pyramidal) coordination.
Spherically arranged inclusions in post-tectonic garnet porphyroblasts
Authors: Harvey P. K. , Ferguson C. C. 
Published: December 2006

SummaryGarnet porphyroblasts, containing elongate ilmenite inclusions arranged in an essentially spherical pattern, are described. The garnets are post-tectonic, and the inclusion pattern is the result of deformation and simultaneous replacement of the matrix by the growing porphyroblast.
The origin and petrogenetic significance of hour-glass zoning in titaniferous clinopyroxenes
Authors: Wass Suzanne Y. 
Published: December 2006

SummaryTertiary alkali basaltic rocks from the Southern Highlands, New South Wales, contain two types of clinopyroxene crystals, which exhibit excellent morphological development of hour-glass zoning. These are small, quench clinopyroxene crystals and large, abundant, euhedral phenocrysts. Electron microprobe analyses show that the different zone sectors derive from compositional differences, with variation in TiO2and Al2O3contents inversely with SiO2content being most significant. Increased depth of colour of titanaugites depends on increased coupled substitution of Al for Si in tetrahedral sites and of Ti3−in anM1site, while pleochroism is enhanced by increasing Fe content. It is suggested that the formation of hour-glass zoning is determined by an environment of crystallization where initial crystal growth is rapid relative to ionic diffusion in the melt, resulting in different chemistry for different growth directions within the crystal. This implies that, under certain conditions, kinetic factors, as well as the chemical composition of the host magma, may be significant in determining the chemical composition of phases precipitated, particularly where more than one crystallographic direction of growth is possible.
The thermal transformation of datolite, CaBSiO4(OH), to boron-melilite
Authors: Tarney J. , Nicol A. W. , Marriner Giselle F. 
Published: December 2006

SummaryA kinetic and X-ray study of the dehydroxylation of datolite, CaBSiO4(OH), has shown that the decomposition occurs very rapidly above 700°C in air, with an activation energy for the reaction of the order of 200 kcal mole −1. The transformation is topotactic, the dehydroxylated phase being tetragonal with a 7·14 Å, c 4·82 Å, and particularly well formed even at the lowest temperatures of decomposition. Single-crystal studies have shown that two orientations of the new phase exist and that the original a of datolite becomes the unique axis of the tetragonal phase while the tetragonal a axes are oriented either parallel to or at 45° to the b and c axes of datolite. The new phase appears to be a boron-containing analogue of the melilite structure, composition Ca2SiB2O7, but is metastable. The basic sheet structure is preserved during the transformation but a reorganization of the tetrahedral layer from the 4- and 8-membered rings of datolite to the 5-membered rings of the new phase is involved, together with effective removal of protons and some silicon. The transformation can be explained in terms of an inhomogeneous reaction mechanism involving migration of calcium and boron into the new phase domains and counter-migration of silicon and protons, but with only minor readjustment of oxygens. The high activation energy of the reaction is explicable in terms either of the effort necessary to remove silicon from the domains of the new phase or of the difficulty of moving the large calcium ions through a relatively close-packed structure.
The crystal structure of julgoldite
Authors: Allmann Rudolf , Donnay Gabrielle 
Published: December 2006

SummaryThe structure of julgoldite, , has been determined and refined to an R value of 4·6 % based on 2417 symmetry-independent reflections, of which 765 are unobserved (weighted R = 4·3 %). The cell dimensions are a 8·922(4), b 6·081(3), c 19·432(9) Å, β 97·60(6)°, the space group is A2/m with Z = 4 and Dcalc 3·56 g cm-3. Julgoldite is isostructural with pumpellyite; the Si-O and Ca-O distances of julgoldite are identical, within experimental accuracy, with corresponding distances in pumpellyite; the Fe-O distances of julgoldite are about 0·09 Å longer than the corresponding (Al, Mg)-O distances in pumpellyite. The four hydroxyl groups and the extent of O-for-OH substitution are identified by valence-sum calculations.
An unusual clinopyroxene with complex lamellar intergrowths from an eclogite in the Sunndal-Grubse ultramafic mass, Almklovdalen, Nordfjord, Norway
Authors: Lappin M. A. 
Published: December 2006

SummaryClinopyroxene crystals with complex lamellar intergrowths of orthopyroxene and garnet are described. The orthopyroxene lamellae are irrationally orientated within the clinopyroxene host although the optical relationships of these minerals are consistent with (100) exsolution in clinopyroxene. The intergrowth is nevertheless considered to be the result of exsolution processes. Possible modes of origin are reviewed together with the general significance of exsolved pyroxenes in eclogite- and granulite-facies associations.
Possible origins of α-damage in diamonds from kimberlite and alluvial sources
Authors: Vance E. R. , Harris J. W. , Milledge H. J. 
Published: December 2006

SummaryHeating experiments provide strong evidence that the transparent green coats on some diamonds from each of many localities are caused by α-particle irradiation after kimberlite injection and subsequent cooling. The natural diamonds with more or less homogeneous transparent green coats, studied in this work, appear to have received doses of at least 5 × 1013−1 × 1014 α.cm−2. For Pre-Cambrian kimberlites, such doses could occur if certain regions of the diatremes contained ⩾20 ppm by weight of equivalent uranium, after kimberlite injection and solidification.Such considerations lead to the prediction that the radioelement concentrations in the Finsch kimberlite diatreme and the Bellsbank fissure kimberlite are considerably greater than those in the Premier mine, though radioelement segregation could produce the required local concentrations. Some exploratory autoradiographic measurements made on two kimberlite rock samples from Premier and De Beers Mines indicated that the radioelements were apparently distributed on a submicron scale, which would be a necessary, but not sufficient, condition for uniform α-irradiation of diamonds.Diamonds from various alluvial sources showing green and brown spots arising from much heavier and more localized radiation damage are also discussed.
Sapphirine-bearing granulitcs from Labwor,
Uganda
Authors: Nixon P. H. , Reedman A. J. , Burns L. K. 
Published: December 2006

Summary
The structural setting of a refoliated
belt of sapphirine granulites in northern Uganda
and petrography of two selected rocks are
described. Electron-probe analyses of the
following minerals are given: ilmenite, titanian
hematite, rutile, magnetite, sapphirine,
hyperstheue, brown and green biotite, garnet, and
cordierite. Field and experimental data suggest
the following paragenesis: deposition of
ferruginous shales with siliceous bands, followed
by burial and regional metamorphism under
granulite facies conditions, and finally rapid
unloading associated with refoliation and shearing
and crystallization of sapphirine and
cordierite.