bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pyroxene and magnetite phenocrysts from the Taupo quaternary rhyolitic pumice deposits, New Zealand
Authors: Ewart A. 
Published: December 2006

SummaryChemical data are presented for four hypersthenes and one coexisting hypersthene-augite pair, and chemical, X-ray, and thermomagnetic data presented for five titaniferous magnetites, all from various horizons of the Taupo pumice sequence. These phenocrysts are regarded as primary crystallization products, and not of xenocrystic origin. The hypersthenes range from Mg46·4Fe51·4Ca2·2 to Mg65·7Fe31·2Ca3·1; the augite composition is Mg48·5Fe12·3Ca39·2. The occurrence of such magnesian pyroxenes may be explained by the early separation of titaniferous magnetite, although it is also possible that the initial iron ratios of the liquids were already sufficiently low to precipitate these pyroxenes.The magnetites exhibit varying stages of oxidation. Data on the least oxidized specimens indicate they were initially magnetite-ulvöspinel solid solutions, with 40 to 50% (mol.) solid solution ulvöspinel. Subsequent oxidation has modified their compositions; there is some evidence that this could have occurred during normal weathering processes.
Structural interpretation of polarized absorption spectra of the Al-Fe-Mn-Cr epidotes
Authors: Burns R. G. , Strens R. G. J. 
Published: December 2006

SummaryMeasurements have been made of the magnetic susceptibility and of the polarized absorption spectra of epidotes of the Al-Fe, Al-Fe-Mn, and Al-Cr series. Magnetic susceptibility measurements at room temperature by the Guoy method indicate that Fe3+, Mn3+, and Cr3+are in ‘high-spin’ electronic states in the epidote structure, and the electronic transitions observed in the absorption spectra have been assigned on this basis. The polarized spectra, measured over the range 4000 to 22 000 Å by a polarizing microscope using a universal stage technique, showed each epidote group to be distinctly pleochroic. This pleochroism correlates with the presence of ions in distorted coordination sites.Extinction coefficients of Fe3+in epidote are higher than those for other Fe (III) compounds, indicating that Fe3+ions occupy the non-centrosymmetric (Al, Fe) site. The low value (13200 cm−1at 0·155 Fe3+and 12700 cm−1at 0·915 Fe3+) of the crystal-field splitting parameter, Δ, implies that the site is easily expanded to accommodate ions larger than Al3+There is also evidence that increasing Fe3+content causes distortion of the (Al,Fe)O6octahedron, suggesting a possible mechanism for the zoisite ⇌ clinozoisite transition.The spectra of Al-Mu-Fe epidotes have been interpreted in terms of intense contributions from Mn3+ions in the non-centrosymmetric (Al, Fe) site, and weak contributions from Mn3+ions in the centrosymmetrie AlOH site. Values of Δ vary from 13730 cm−1(0·082 Mn3+) to 13400 cm−1(0·747 Mn3+). Both (Al, Fc) and AlOH sites have strong tetragonal distortions (c/a~ 0·95), leading to the observed large Jahn-Teller splitting of 12000 cm−1.The Al-Cr epidote spectra show weak absorption bands, attributed to Cr3+ions in a centrosymmetric site of approximately orthorhombic symmetry (i.e. the AlO site). The value of Δ is about 16300 cm−1.Review of all available data on the distribution of Fe3+, Mn3+, and Cr3+between the sites gives the following site preferences: Fe3+, Al > AlO > AlOH; Mn3+, Al ≥ AlOH ≫ AlO ; Cr3+, AlO ≫ Al, AlOH.
A second occurrence of dalyite and the petrology of some ejected syenite blocks from São Miguel, Azores
Authors: Cann J. R. 
Published: December 2006

SummaryDalyite, K2ZrSi6O15, occurs in the ejected syenite blocks of Serra de Agua de Pau (Lagoa do Fogo), São Miguel, Azores, in an assemblage sanidine-arfvedsonite-quartz-aegirine-fayalite-astrophyllite-dalyite-pyrrhite. Other blocks from the same locality contain biotite-zircon in place of astrophyllite-dalyite. A comparison made between the chemistry of one specimen of each type indicates that they may be related by paraeutectoid fractional crystallization.
Influence of light reflection at the objective in the quantitative measurement of reflectivity with the microscope
Authors: Filler Horst 
Published: December 2006

SummaryWhen the microscope is used in the measurement of reflectivity there is a glare effect, due to internal reflections from optical parts, for which corrections have to be made. In the present paper these effects are measured in a new series of objectives for reflected-light microscopes, and it is shown that the factors involved are the number, curvature, separation, and blooming of the lenses, along with the conditions of adjustment of the microscope. For a given objective the conditions producing the smallest glare are: small area of specimen illuminated and measured, high numerical aperture of the illuminating system, and adjustment of the illuminaton in such a way that the axis of the illuminating beams is slightly oblique. A theory of glare is outlined, and procedures for making the necessary corrections are described—by calculation and by graphical procedure. These corrections can be neglected when a sufficient number of graded standards is used.
A note on the occurrence of potassium-rich trachytes in the Kaiserstuhl carbonatite complex, West Germany
Authors: Sutherland D. S. 
Published: December 2006

SummarySpecimens of trachyte obtained on a recent visit to the Kaiserstuhl are compared with similar potassium-rich rocks from carbonatite complexes in Africa. Two new chemical analyses are given, in which the values for alkalis (Na2O 1·21, K2O 12·63; Na2O 0·92, K2O 12·18 %) are of interest.
Potash-rich volcanic rocks from southern Spain
Authors: Borley G. D. 
Published: December 2006

SummarySeveral restricted outcrops of potash-rich volcanic rocks occur in the Spanish provinces of Murcia and Almeria, where they form intrusive pitchstones or surface lavas among country rocks consisting of Tertiary and Quaternary sediments: the volcanic rocks include jumillites and verites from the type localities of Jumilla and Vera and it is these rocks that have been investigated. Jumillites are basic lavas, sometimes coarse-grained, rich in MgO, CaO, K2O, TiO2, and P2O8, poor in SiO2, Al2O3, and Na2O and they contain important, if minor, concentrations of Cr2O3, BaO, SrO, and ZrO2. Their mineralogy is distinctive: chrome diopside, forsterite, titaniferous phlogopite, kataphorite, and sanidine, with rare leucite. Verites, typically, are black pitchstones or pitchstone breccias that range from basic to acid in composition ; they are more variable in their chemistry than jumillites, but in part this variation might be due to introduction of silicate and carbonate into some of the verites during extensive hydrothermal alteration, which has undoubtedly affected their initial chemistry. Mineralogically, verites are simpler than jumillites and have fewer phenocrysts: forsterite, some diopside, phlogopite, and, occasionally, leucite. Certain mineralogical and compositional similarities of jumillites and verites suggest they may have originated from the same type of parental magma. Their mineralogy and chemistry also relate the jumillites and verites to phlogopite-bearing potash-rich volcanics from East Africa, America, and Australia and it seems possible that all these rocks might have a common parent in mica peridotite or mica pyroxenite.
A garnet peridotite and a garnet-amphibole pyroxenite from South Harris, Outer Hebrides, and their bearing on the South Harris eclogite facies status
Authors: Livingstone A. 
Published: December 2006

SummaryA garnet-olivine metaperidotite and a garnet-amphibole pyroxenite are described. Chemical analyses are presented for six rocks and optical properties and chemical analyses are tabulated for clinopyroxene, almandine-pyrope garnet, and hastingsitie amphibole from the garnet-amphibole pyroxenite. A possible origin for the garnet peridotite and chemically similar granulite facies ultramafic rocks is suggested. The eclogite facies in South Harris is reinstated in the light of the data presented.
The miscibility of the pyralspite and grandite molecules in garnets
Authors: Němec D. 
Published: December 2006

SummaryThough the transitional members between the pyralspite and grandite series occur only very sporadically, there exists under favourable conditions a perfect miscibility between grossular on the one hand, and spessartine or almandine or pyrope on the other. The conditions favouring this miscibility are discussed.
Alkaline-earth-rare-earth silicate and germanate apatites
Authors: Cockbain A. G. , Smith G. V. 
Published: December 2006

SummaryA number of new alkaline-earth-rare-earth silicate and germanate compounds with the apatite-type structure have been synthesized including a new calcium lanthanum silicate, Ca4La6(SiO4)6(OH)2, which has a 9·63 Å, c 7·12, and c/a 0·740. This has a random distribution of Ca2+ and La3+ over the (4f) and (6h) sites in the lattice. X-ray data are given for Ca4La6(SiO4)6(OH)2 together with cell dimensions for other synthetic silicate and germanate apatites. Silicate apatites with partially occupied or vacant halogen (2a) sites analogous to those of the pyro- morphites have been prepared, and a classification for silicate apatites based on synthetic end-members is proposed.
The nature of ‘ameletite’
Authors: Coombs D. S. , Wilkinson J. F. G. 
Published: December 2006

SummaryOriginally described in phonolitic rocks from the Dunedin district, New Zealand, ameletite was considered by Marshall (1929) to be a chlorine-bearing sodium aluminium silicate, probably a feldspathoid, and later, a zeolite of unspecified composition. Optical, X-ray, and chemical data on several ‘ameletite’-bearing felsic volcanic rocks from the type area indicate that material previously designated as ameletite is variously nepheline and mixtures of sodalite, analcime, phillipsite, and nepheline. Criteria thought to be characteristic of ameletite are discussed.
Electron-probe microanalysis of coronas in a troctolite from Sulitjelma, Norway
Authors: Mason Roger 
Published: December 2006

SummaryThe results of the electron-probe microanalysis of the three minerals from orthopyroxene-amphibole-spinel coronas between olivine and plagioclase in a troctolite from Sulitjelma, Norway, are presented. They are shown to be incompatible with a late-magmatic origin for the coronas, but compatible with an origin by diffusion of material in solution in an aqueous medium across the olivine-plagioclase interface. This theory is discussed on a quantitive basis in the light of the microanalytical data.
‘Plumbogummite’ from Roughten Gill Cumberland
Authors: Förtsch E. B. 
Published: December 2006

SummaryX-ray, infra-red, and optical studies suggest that the bluish-grey crust (previously described as plumbogummite) on arsenian pyromorphite from Roughten Gill, Cumberland, is a carbonate-bearing mix-crystal of plumbogummite, hinsdalite, and hidalgoite with a 7·018 Å, c 16·784 Å; arh 6·907, a 61° 3′; ω 1·680, ɛ 1·698.
Symmetry–entropy–volume relationships in polymorphism
Authors: Strens R. G. J. 
Published: December 2006

SummaryGroup theoretical analysis of the normal vibrations of isolated molecules and of macroscopic crystals indicates that the principal effect of symmetry reduction is to remove the degeneracy of the normal vibrations, thus reducing the number of microscopic complexions of the phonon distribution, and reducing the entropy. This mechanism is effective only in point groups containing a rotation axis of order 3 or greater, and may play a part in the high-low cordierite transition.Two other symmetry-related entropy contributions are discussed : the first is the loss of positional degeneracy in systems in which the number of available positions exceeds the number of atoms, as in high-low quartz, vlasovite, and many ferroelectrics. The second is the loss of positional degeneracy in a solid solution, which leads to unmixing, as in high-low albite, microcline-sanidine, and high-low cordierite transitions. These mechanisms are effective in all point groups down to 1 =C1, and can proceed even withinC1by a change in the unit cell volume.Consideration of entropy-volume relationships suggests that the glaucophane I–II transition has less order-disorder character than previously supposed. It is suggested that zoisite-clinozoisite, anthophyllite-cummingtonite and enstatite-clinoenstatite relationships are polytypic rather than polymorphic in the usual sense, and the mechanisms responsible for producing the stacking order are discussed.The implications of the differences between the behaviour of the classical double oscillator (often used as a model for displacive transitions) and its quantized analogue are discussed.
Δ2θ131-13̄1 for albites crystallized in the systems NaAlSi3O8–β-LiAlSi2O6-H2O and NaAlSi3O8-LiAlSiO4-H2O
Authors: Edgar A. D. , Piotrowski J. M. 
Published: December 2006

SummaryValues of Δ2θ131-13̄1(Cu-Kα) have been determined for albites crystallized in the system NaAlSi3O8-β-LiAlSi2O6-H2O at various pressures, temperatures, and times. These values are consistently higher than those reported by MacKenzie (1957) for pure synthetic albites crystallized under similar conditions. Data of the present study have been combined with that of Stewart (1960) for albites crystallized in the system NaAlSi3O8-LiAlSiO4-H2O and, when plotted against bulk Li2O content, show constant Δ2θ131-13̄1 values at approximately 1·0 wt. % Li2O. The addition of Li to albites has a much more pronounced effect on the Δ2θ131-13̄1 parameter than the addition of K or Ca. Albites from lithium-rich pegmatites have much lower Δ2θ131-13̄1 values and are similar to those of synthetic low albites. The differences in this parameter between the natural and synthetic specimens are believed to be caused by differences in the structures of the coexisting lithium minerals in the natural and synthetic environments.
An X-ray investigation of green mica in khondalite from Auranga-Koel Valley, Palamau, Bihar, India
Authors: Gupta M. P. , Gupta N. P. 
Published: December 2006

SummaryA new variety of chrome mica containing V2O3 and TiO2 has been investigated by X-rays. It is shown that the crystals of this mica are monoclinic with a= 5·25 Å, b = 9·03 Å, c = 20·11 Å, β = 96·00′, space group C 2/c. Comparison of the intensities of the X-ray powder lines of this new variety of mica with that of pure muscovite may indicate structural changes. The optical properties and chemical composition of the mica are described.
The mineralogical composition and structure of the Assisi meteorite
Authors: Levi-Donati G. R. 
Published: December 2006

SummaryThe principal data about the fall and the distribution of the fragments of the Assisi (Perugia, Italy) meteorite are collected. A fragment of the stone, weighing 146·5 g, preserved in the British Museum (Natural History) (B.M. 63621), is described in some detail. Crust morphology, mineralogical composition, and structure are studied. Optical data are established by microscopical analysis of five thin sections and two polished surfaces. Compared with electron-probe analysis, they are found in good agreement. Assisi is an olivine-bronzite chondrite, H group, with characteristic features of metamorphism.
The crystal structure of parahopeite
Authors: Kumbasar Isik , Finney J. J. 
Published: December 2006

SummaryParahopeite, Zn3(PO4)2.4H2O, is the triclinic dimorph of hopeite. The crystal structure of parahopeite has been determined to be similar to phosphophyllite, Zn2Fe(PO4)2.4H2O and to hopeite in that one of the two zinc atoms is six-coordinated and the other is four-coordinated. Parahopeite differs from the other two minerals though because one of the P-O tetrahedral oxygen atoms is bonded to both the six- and the four-coordinated cations. That is, all four tetrahedral oxygen atoms are bonded to the four-coordinated zinc in parahopeite, whereas in phosphophyllite and hopeite only three of these oxygen atoms are so bonded.
Preferential crystal growth along tilt and twist boundaries in hematite
Authors: Sunagawa Ichiro 
Published: December 2006

SummaryEvidence of preferential crystal growth along tilt and twist boundaries was observed on a hematite crystal from St. Gothard, Switzerland. Irregular lines that cut across the triangular growth layers on the (0001) face develop around a misoriented hematite crystal. There is a slight inclination of the surface on both sides of the lines, suggesting that they are small-angle grain boundaries (tilt and twist boundaries), consisting of screw and edge dislocations. Both spirals and triangular terraces occur along these lines, in addition to the original triangular growth layers. Growth spirals are also present on the (101̄1) faces, distributed along certain lines. From these observations it is concluded that preferential crystal growth took place, during the final stage of growth of the host crystal, at both screw and edge dislocations in the tilt and twist boundaries. The latter were formed by the impinging of another hematite crystal on the growing surface of the host crystal.
Further discussion of framework structures built from four- and eight-membered rings
Authors: Smith J. V. 
Published: December 2006

SummaryThe classification of framework structures built from chains of four-membered rings of type UUDD is incomplete: there are two basic ways in which the chains can be cross-linked to form eight-membered rings. The first type of frame-work (already described) is extremely flexible, permitting the cavities to be either large or small; the second type is inflexible and the cavities are small. Feldspar belongs to the second type and had been incorrectly ascribed to the first type: paracelsian, harmotome, and gismondine had been correctly placed in the first group.
On the composition of delafossite
Authors: Wiedersich H. , Savage J. W. , Muir A. H. , Swarthout D. G. 
Published: December 2006

SummaryOxides of the Cu-Fe-O system prepared by solid-state reaction methods have been investigated by X-ray, Mössbauer effect, and analytical chemical techniques. In agreement with most previous investigations of this system, it is found that CuFeO2 exists as a stable compound, and that the mineral delafossite has essentially this composition. These results are in disagreement with those of Buist, Gadalla, and White who propose that delafossite has an approximate composition Cu6Fe3O7 instead of CuFeO2. In fact, a compound of composition Cu6F3O7 could not be prepared. The Mössbauer isomer shift provides confirmation that the iron in CuFeO2 is trivalent.
The crystal chemistry of the apatites
Authors: Cockbain A. G. 
Published: December 2006

SummaryThe compositions of more than eighty synthetic members of the apatite group with the general formulaA10(XO4)6Z2have been used as a basis for classifying the apatites into three groups. The ratios of the mean sizes of the ‘A’ ions to those of the ‘X’ ions for all these compositions lie between the limits of 1·89 and 4·43. A discontinuity occurs between ratios of 2·50 and 2·60 and probably another between 3·25 and 3·35, and these discontinuities provide a structural basis for the division into the three groups. The groups are named after well-known mineral species occurring in each group, i.e. the vanadinite-svabites with anA:Xratio less than 2·5, the apatite-mimetites between 2·60 and 3·25, and the pyromorphites withA:Xgreater than 3·25.
Genetic significance of trace elements in certain rocks of Singhbhum, India
Authors: Mukherjee Bibhuti 
Published: December 2006

SummaryThe distribution of trace elements is studied in different acid and basic rocks, adjacent to the copper lodes in the Mosaboni mines, Singhbhum, and adjoining the thrust zone, as well as of areas far away from the mineralized zones. Specific differences in composition and trace constituents in these rocks especially as regards S, Cu, Ni, and Co, suggest that the relationship of the Singhbhum granite with the soda granite is most unlikely, and that there is a connection between the soda granite and the sulphide ore-fluid ; a genetic relationship of sulphide mineralization with the epidiorite is doubtful. The possibility of the existence of a common source for the Chotanagpur granite and the Singhbhum granite is inferred.
New stony meteorite finds including two ureilites from the Nullarbor Plain, Western Australia
Authors: McCall G. J. H. , Cleverly W. H. 
Published: December 2006

SummaryTwo groups of meteorite finds in separate areas of the Nullarbor Plain are reported. It is suggested that the grouping is due to the fact that these are areas in which a family of rabbit trappers operates: these people have made most of the finds. There is, however, one shower of 71 small meteorites represented. Several arrivals on earth are represented by each group. The meteorites are described and it is shown that several distinct types are represented. Two quite different ureilites have been identified—only the fourth and fifth ever discovered in the world. Analyses are given for these rare carbonaceous achondrite meteorites. The remainder of the stones are olivine-hypersthene and olivine-bronzite chondrites. The whole question of the reason for the profusion of meteorite recoveries now being made on the Nullarbor Plain is briefly discussed.
The role of titanium and the effect of TiO2 on the cell-size, refractive index, and specific gravity in the andradite-melanite-schorlomite series
Authors: Howie R. A. , Woolley A. R. 
Published: December 2006

SummaryNew chemical analyses, cell-sizes, and specific gravities are given for 12 garnets, and TiO2 values, cell-sizes, and refractive indices are presented for a further 33 garnets all belonging to the andradite-melanite-schorlomite series. The increase of refractive index, cell-size, and specific gravity with increasing titania is shown graphically. A plot of Ti against Si atoms in the unit cell suggests that Ti replaces Si rather than Fe3+ in the structure, while electron-probe results indicate that Si or (Si+Fe) may be replaced by Ti. The chemical and infra-red absorption data are considered in a discussion of the structural role of titanium in these garnets : both Ti4+ and Ti3+ may be present.
Zoned plagioclase from the charnockites of Kondapalli, Krishna district, Andhra Pradesh, India
Authors: Leelanandam C. 
Published: December 2006

SummaryZoning in plagioclase is reported from the charnockitic rocks of Kondapalli, Krishna district, Andhra Pradesh, India, for the first time. Electronprobe studies indicate that the zoned plagioclases consist of homogeneous sodic cores mantled by thin calcic shells, which show continuous zoning of the inverse type. Partial chemical analyses of twelve density fractions of the zoned plagioclase from a basic charnockite exhibit a wide variation in An content from 54·80 to 72·39 %; X-ray studies suggest that they possess ‘fixed’ transitional structural state.
The preparation of silicate compositions by a gelling method
Authors: Hamilton D. L. , Henderson C. M. B. 
Published: December 2006

SummaryA method for the preparation of chemically homogeneous powders by a weighing and gelling technique is described in detail. Stress is placed on the importance of the weight yield as an indication of the bulk chemical composition and on the chemical analysis of several portions to test the homogeneity. A list of recommended chemicals is included in an appendix.