bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron-probe micro-analysis of the iron–titanium oxides in some New Zealand ironsands
Authors: Wright J. B. , Lovering J. F.
Published: December 2006

The electron probe was used to analyse for Fe, Ti, Mg, Al, and Mn. Vanadium could not be determined because of interference from Ti. Calcium was shown to be present only in inclusions of apatite and silicate; it does not oceur in the titanomagnetite structure.

Homogeneous grains (magnetite-ulvöspinel solid solutions) do not vary greatly in bulk composition, averaging close to 61% Fe and 8 % TiO2. Inhomogeneous grains contain variable amounts of hematite-ilmenite lamellae produced by progressive oxidation of the homogeneous grains. In the early stages there is rapid build-up of titanium in the rhombohedral lamellae, which are initially relatively poor in iron. As oxidation proceeds the almost titanium-free cubic phase becomes strongly enriched in magnesium, aluminium, and manganese, while the iron: titanium ratio in the rhombohedral phase increases. The end-product may be a homogeneous titanhematite, if initial concentrations of Mg, Al, and Mn are low. Otherwise residuals of a relatively iron-poor almost titanium-free (Mg, Al, Mn)-enriched cubic phase remain in the titanhematite. The behaviour of iron and titanium agrees with recent synthetic work in the system. Some of the oxidized grains contain transparent spinel lamellae exsolved from the cubic phase. Exsolution may commence at different stages in the oxidation process, but the reason is not clear—there are no significant differences in the composition of phases with and without spinel lamellae.

Analyses and normative compositions are presented for the different phases in each grain, where possible. The compositional changes accompanying oxidation satisfactorily explain the slope of the thermomagnetic curves : there is no need to invoke bulk compositional variations within a given ironsand sample.

Samples from an ilmenite and a non-titaniferous magnetite concentrate were also briefly examined.
A note on varlamoffite and associated minerals from the Batang Padang district, Perak, Malaya, Malaysia
Authors: Alexander J. B. , Fliter B. H.
Published: December 2006

A new occurrence of varlamoffite is described, and the status of this species is considered; the term is best employed for cryptocrystalline yellowish material consisting predominantly of Sn and H20 that may yield a diffuse powder pattern comparable to, or closely resembling that of cassiterite, but does yield a powder pattern identical with that of cassiterite after heat-treatment at about 1200° C. A new mineral, malayaite, CaSnSiO5, is briefly described; it is isostructural with sphene.
The origin of accessory garnet in the Donegal Granite
Authors: Hall Anthony , Tyler R. C.
Published: December 2006

In the Donegal Granite garnet occurs as an accessory mineral in muscovite-granties, pegmatites, and aplites. The composition of the garnet in fourteen samples of granitic rock has been determined from the physical properties and three new chemical analyses are given. All the samples examined are intermediate in composition between almandine and spessartine. The reason for the high manganese content in garnet from granites is discussed.
Kamacite plate width estimation in octahedrites
Authors: Frost M. J.
Published: December 2006

Tables are given which enable a quick estimate to be made of the true thickness of kamacite plates from measurements of the Widmanstetter figure on a single random plane. The method is applied to the following meteorites (width in mm following name): Arispe, 2·90; Brenham, 0·91; Duketon, 1·13; Henbury, 0·74; Ogallala, 1·53; Thule, 0·89; View Hill, 0·62.
The petrographic use of the spindle stage and focal-plane screening in the determination of the optical variation of some zoned minerals
Authors: Wright Hedley G.
Published: December 2006

The Equivibration Curve technique of Joel (1963) is used to determine the orientation of a zoned mineral on the spindle stage axis and an average value for 2V. A bracketing method enables the extreme values of each refractive index to be determined for sodium light on a single grain, using the Focal-plane Screening technique of Cherkosov (1960).
A note on the 01 spacing of some lime-rich alkali feldspars from Kangerdlugssuaq, East Greenland
Authors: Kempe D. R. C.
Published: December 2006

The values of 2θ 01 for some homogenized lime-rich fine microperthites from the Kangerdlugssuaq alkaline intrusion, East Greenland, are investigated and found to be consistently high when compared with the values used in the standard curves for estimating the Or content of alkali feldspars. This deviation, which is approximately proportional to anorthite content, results in anomalously low Or percentages being obtained and is ascribed to a distortion of the structure due to the unusually high calcium content of the microperthites.
The measurement of large optic axial angles with the universal stage
Authors: Munro M.
Published: December 2006

A comparison has been made of the relative speed, accuracy, and precision of several methods of measuring large optic axial angles with the universal stage. It is concluded that a method based on the direct location of a single optic axis and the application of the Biot-Fresnel law will frequently be the most satisfactory when only the standard, low refractive index centre plate for the stage is available. If a centre plate of high refractive index is employed, however, good results can normally be obtained by using the more rapid method based on the direct location of both optic axes.
Secondary clay in Rajmahal basalts of India and its relation to palagonite-chlorophaeite
Authors: Sarbadhikari T. R. , Bhattacherjee Santi
Published: December 2006

The mineralogy of the green, yellow, and brown secondary constituents occurring as amygdales, irregular infillings, and replacements in the Rajmahal basalts of eastern India and commonly described under the ill-defined names palagonite and chlorophaeite, has been revised on the basis of optical, X-ray, and thermal studies. The results indicate that these coloured constituents, which have been chiefly derived by the alteration of pyroxenes, iron ores, and primary glass, belong to the clay minerals, particularly smectite and vermiculite. This brings in question the validity of the terms palagonite and chlorophaeite which, though widely current in basaltic literature, have no definite mineralogical identity. It is suggested here that they are but forms of clay.
Unit cell volumes of synthetic orthoenstatite and low clinoenstatite
Authors: Stephenson D. A. , Sclar C. B. , Smith J. V.
Published: December 2006

Cell dimensions and densities derived from least-squares refinement of X-ray powder diffractometer patterns are: orthoenstatite, a 18·2249±0·0013, b 8·8149±0·0008, c 5·1746±0·0008 Å, V 831·30±0·14 Å3, D 3·208 g/cc ; low clinoenstatite, a 9·6065±0·0011, b 8·8146±0·0007, c 5·1688±0·0006 Å, β = 108·335± 0·009, V 415·46±0·09 Å3, D 3·210 gm/cc. Because orthoenstatite transforms reversibly to clinoenstatite at high pressure and low temperature, and because a statistical test shows that orthoenstatite is less dense than clinoenstatite at the 90 % confidence level (in accord with the direction of slope of the experimental transition curve), it is no longer possible to regard low clinoenstatite as a metastable form of MgSiO3.
Residual glasses from some alkali basaltic lavas from New South Wales
Authors: Wilkinson J. F. G.
Published: December 2006

The glassy residua from an alkali olivine-basalt and a nephelinebasanite are respectively alkali trachytic and phonolitic in composition and contrast strongly with the compositions of the host rocks. The analysis of the glass from the alkali olivine-basalt reveals appreciable normative corundum, which is considered a consequence of the crystallization of excessive diopsidic clinopyroxene. This results in a deficiency in lime relative to alumina during the crystallization of much of the plagioclase. A consideration of the compositions of the glasses and the salic differentiates from alkaline basic intrusions indicates that the development of either trachyte or phonolite depends on differing degrees of undersaturation of the parental basic magmas.
On the oriented conversion of Ca(OH)2 to CaO
Authors: Chatterji S. , Jeffery J. W.
Published: December 2006

In order to study the orientational relationship between Ca(OH)2 and CaO, the transformation was carried out in stages inside an electron microscope by condensing the electron beam, and the process was monitored by electron diffraction. It has been found that at the initial stage all the hexagonal spots of Ca(OH)2 split into two ; on further heating one set of spots disappear. The remaining set of spots corresponds to the CaO structure, which has an orientational relationship to the hydroxide structure. To estimate the degree of orientation, a sample of brucite was treated in a similar way to the Ca(OH)2; a comparison shows that a high degree of orientation is preserved in the conversion of Ca(OH)2 to CaO. This observation is contrary to earlier reports.
The Barwell meteorite
Authors: Jobbins E. A. , Dimes F. G. , Binns R. A. , Hey M. H. , Reed S. J. B.
Published: December 2006

Part of a meteorite was seen to fall on a road (52° 33′ 55″ N., 1° 20′ 23″ W.) in the village of Barwell, Leicestershire, at about 16.20 hrs G.M.T. on 24 December 1965. Fragments have been found over an area some ¾ mile long by ½ mile across, and appear to have been part of a single stone, of which 44 Kg (97 lb) have been recovered. The distribution, impact effects, and crustal morphology of the recovered fragments are described. Barwell is a moderately metamorphosed white olivine-hypersthene chondrite; a chemical analysis, with the derived Wahl norm, and a modal analysis are given, together with optical data and electron-probe analyses of the principal constituent minerals.
The dehydroxylation behaviour of amphiboles
Authors: Freeman A. G.
Published: December 2006

The temperature at which dehydroxylation occurs in amphiboles is thought to be largely dependent on the type of cation that occupies the M3 and M1 sites. Four amphibole types have been studied in which these sites are occupied, in various proportions, by Mg2+ or Fe2+. The temperature of dehydroxylation, in an inert atmosphere, is shown to rise with increasing Mg2+ content in these sites.
A simplified method of 2 V determination using 3- and 4-axis stages
Authors: Ehlers Ernest G.
Published: December 2006

A method is presented for use with a 3- or 4-axis stage whereby a biaxial mineral, after being oriented into the cardinal position by means of the inner vertical, NS., and EW. axes, can be placed into an orientation suitable for measurement of the 2 V as required by the Berek method. A table of the necessary manipulations is given. The stereographic projection is only used to determine rotational corrections.
Psilomelane from India
Authors: Mukherjee Bibhuti
Published: December 2006

Mukherjee's definition of psilomelane, A3X6Mn8O16 of orthorhombic symmetry with the space group P222 and the dimensions determined for a single crystal of the Schneeberg sample, is found true for the psilomelane from Ratanpur, India. The indexing of powder data of the Ratanpur sample with the orthorhombic axes a 9·45, b 13·90, c 5·72 Å is most satisfactory.
Sideronatrite from mineralized cavities in the Rising Sun colliery, Backworth, Northumberland
Authors: Randall B. A. O. , Jones J. M.
Published: December 2006

Two unusual cavities at a Northumberland colliery are described. Although apparently of tectonic origin they do not seem to be related to any major fault. Sideronatrite, not previously recorded in this country, is thought to result from the alteration of the marcasite and pyrite lining the cavities by underground saline waters. These waters are the source of the baryte and gypsum that are also found in the cavities and of the salt stalactites in the disused roadways of the colliery.
Rhodonite from Meldon, Okehampton, Devonshire
Authors: Dearman W. R.
Published: December 2006

There are two outcrops of rhodonite rock at the same stratigraphical horizon in Lower Carboniferous rocks in the Railway Quarry at Meldon. One of these is zoned outwards from rhodonite, through calc-silicate hornfels to quartzite. Well-formed crystals occur in drusy massive rhodonite; examples have been measured and drawn.
Externally heated cold-seal pressure vessels for use to 1200° C at 1000 bars
Authors: Williams D. W.
Published: December 2006

Apparatus using cold-seal pressure vessels of molybdenum-0·5 %-titanium alloy, where each vessel is protected from oxidation by an argon gas jacket, is described. At 1000 bars pressure these vessels can be used for long runs at temperatures up to 1200° C, an increase of approximately 300° C over the range of conventional Stellite vessels. The possible use of other alloys to extend the range of this type of apparatus further is briefly discussed; pure tungsten has been shown to be too brittle.
A new British locality for beudantite: Sandford Hill, Somerset
Authors: Livingstone A. , Cogger N.
Published: December 2006

A new British locality for beudantite [PbFe3(AsO4)(SO4)(OH)6] is recorded. The mineral is intimately associated with goethite; chemical, d.t.a., and thermogravimetric analysis data for the mixture are presented and a possible paragenesis suggested.
The petrology of the Mount Padbury mesosiderite and its achondrite enclaves
Authors: McCall G. J. H.
Published: December 2006

The petrography of the Mount Padbury meteorite, previously briefly recorded, is described in some detail. Both the metalliferous host material of the mesosiderite and the varied range of silicate-rich, virtually metal-free enclaves (including both familiar achondrite material and unfamiliar achondrite material) are described. Eucrite, brecciated eucrite, and a peculiar ‘shocked’ form of eucrite (resembling some terrestrial flaser-gabbros) are the calcium-rich achondrite types represented; hypersthene achondrite (including typical diogenite material and unfamiliar material) and olivine achondrite (granular aggregates of olivine not entirely similar to the unique chassignite and single crystals up to 4 in. in length) are the calcium-poor achondrite types represented. The eucrite displays more or less uniform mineralogy, but the mineral constituents are present in varying proportions, and there is a wide range of textural variations recognized. The silicate grain fragments enclosed in the metallic reticulation to form the mesosiderite host material are, significantly, entirely of minerals seen within the achondrite enclaves—plagioclase, hypersthene, pigeonite, olivine, and tridymite.

These results include microscopic analysis of thin sections and polished sections, X-ray diffraction studies, optical determination of refractive indices using mineral grain mounts, and chemical analyses.

The wider implications of this new and unique meteorite find are briefly considered.
On the existence of hydronium hydrates H9O+4 and H15O+7 in minerals
Authors: Kubisz Jan
Published: December 2006

Properties and possible structures of hydronium trihydrate H9O+4 and hexahydrate H15O+7 are considered. From the 2330 minerals listed in Strunz's mineralogical tables nineteen were selected that appear to contain H+.4H2O or H+.7H2O, and the possibility of discrete H9O+4 or H15O+7 groupings existing in their crystal lattice is discussed. From a crystallochemical point of view the most probable examples of hydronium hydrate compounds are layer lattice minerals like H-montmorillonite, H-vermiculite, troegerite, H-meta-autunite, sabugalite, and hewettite.
On the preferred crystallographic orientation of garnet in some metamorphic rocks
Authors: Powell Derek
Published: December 2006

A study of inclusions within garnet porphyroblasts demonstrates that planar inclusion bands and trails lie sub-parallel to one of the {110} planes of the host. The inclusions provide a relic of a rock fabric that existed before the growth of garnet. It is suggested that this fabric has determined the crystallographic orientation of garnet and may have arisen by the nucleation and epitaxial growth of garnet within or upon the mica lattice.
Heating experiments on gudmundite
Authors: Horrell Clark A.
Published: December 2006

In the absence of published experimental data on phase equilibria in the ternary system Fe-Sb-S and on the stability relations of gudmundite (FeSbS) and berthierite (FeSb2S4) , some preliminary investigations on the upper stability limit of natural gudmundite are briefly described. On heating in vacuo, As-free gudmundite broke down between 269° and 288°C, an approximate upper stability limit of 280±10°C conforming to the stability relations of the associated phases.
Anandite, a new barium iron silicate from Wilagedera, North Western Province, Ceylon
Authors: Pattiaratchi D. B. , Saari Esko , Sahama Th. G.
Published: December 2006

Anandite is a new barium iron silicate found in the magnetite ore zone of the Wilagedera iron ore body, in the North Western Province of Ceylon. The mineral is named after the late Dr. Ananda Coomaraswamy, the first director of the Mineral Survey of Ceylon.

Anandite is monoclinic, with a 5·412, b 9·434, c 19·953 Å, β 94° 52′, space group C2/c. D 3·94, hardness 3–4. Optically positive, b ‖ β, γ ∧ a 12°, β 1·855, γ > 1·88. Pleochroism: β green, γ brown. Chemical composition corresponds to the simplified formula (Ba,K) (Fe,Mg)a (Si,Al,Fe)4O10 (O,OH)2 with Z = 2. The data available indicate that the mineral has the trioctahedral structure of the brittle micas.
The pyroxenes of the alkaline igneous complexes of eastern Uganda
Authors: Tyler Ruth C. , King B. C.
Published: December 2006

Chemical analyses, some optical data, and specific gravities are given for 57 pyroxenes from the alkaline rocks of Uganda. They are members of the diopside-hedenbergite-acmite series, the more diopsidic varieties occurring in rocks of the ijolite series and the more acmitic in syenites and carbonatites. TiO2 is highest in those pyroxenes from rocks that do not contain melanite. The refractive indices and specific gravities are controlled by the Fe2+/Mg ratio in the diopsidic pyroxenes and by the Fe3+ content in the acmitic members. Paragenesis is discussed briefly.
The mechanism of oxidation in titanomagnetites: a magnetic study
Authors: O'Reilly W. , Banerjee Subir K.
Published: December 2006

A hypothesis for the mechanism of oxidation in titanomagnetites is first put forward on the basis of new oxidation data for pure magnetite and the new model for cation distribution in titanomagnetites. Contrary to previous claims by other workers, it is shown that single-phase spinel oxidation products of titanomagnetites can only be produced under very exacting circumstances. Lowtemperature magnetic measurements on such synthetic, oxidized materials were made to show the formation of magnetite by the decomposition of the metastable oxidation products of titanomagnetites on prolonged heating at moderate (∼ 390° C) temperatures. This magnetic method of detection is more sensitive than that of normal X-ray diffraction. It is concluded that previous claims of an increase in magnetization due to the formation of synthetic single-phase, highly oxidized titanomagnetites must be due to the formation of undetected magnetite.
The crystal structure of gersdorffite
Authors: Bayliss P. , Stephenson N. C.
Published: December 2006

Gersdorffite belongs to space group P213 in the cubic system with cell dimension a 5·6885 ± 0·0003 Å and four formula units per cell. The hk0 data were measured from precession photographs obtained with Mo-Kα radiation. The structure was solved by Patterson methods and refined by least-squares techniques. This structure has complete ordering of arsenic and sulphur similar to ullmannite.
A heulandite with excess water
Authors: Wise William S.
Published: December 2006

A heulandite from Nelson Creek, Skamania County, Washington, has 30 H2O per unit cell instead of the normal 24; the excess water is lost on gentle heating. The b and c cell-dimensions are also rather larger than normal. Normal heulandite also occurs in the same area.
X-ray studies of natural fabrics: I. Growth-fabrics in hematite kidney ore and in fibrous calcite
Authors: Bradshaw R. , Phillips F. C.
Published: December 2006

Fibres of hematite in kidney ore are elongated at right angles to thec-axis. The fibre axis, which may be normal to a face of either of the hexagonal prisms {101̄0} or {112̄0}, may show an abrupt change of orientation along the length of a fibre. There is little preferred orientation around the length of the fibres.

It is confirmed that in some calcite satin spar the fibres are elongated parallel to an edge of the cleavage rhombohedron; in other fibrous growths the elongation is either parallel to or Perpendicular toc.
A note on monalbite
Authors: Hall K. M. , Quareni S.
Published: December 2006

Attempts to reproduce the X-ray measurements which led W. L. Brown to postulate the existence of monalbite at room temperature were unsuccessful.
A reinterpretation of monalbite
Authors: Brown William L.
Published: December 2006

A neutron activation analysis of one of the crystals of ‘monalbite’, which was monoclinic at room temperature, shows that it contains a large proportion of potassium. It is thus not a polymorph of pure NaAlSi3O8. The contamination occurred by transfer of K through the atmosphere of the furnace from potassium-bearing ceramic materials.
On the existence of monoclinic NaAlSi3O8 s at elevated temperatures
Authors: Grundy H. D. , Brown W. L. , MacKenzie W. S.
Published: December 2006

Measurements from powder diffraction patterns recorded at temperatures up to 950° C for the supposed equilibrium forms of albite synthesized at 800°, 900°, and 1000° C by MacKenzie (1957) indicate that only the form synthesized at 1000° C becomes monoclinic. Single-crystal measurements on heated pure natural albite (Ab99·26) show that it becomes truly monoclinic, both in geometry and intensity distribution, at 930° C, the same temperature as for the highest-temperature synthetic form. These experiments were carried out in conditions that exclude possible contamination by potassium.
Extinction curves and equivibration curves obtained with a variable-axis spindle-stage
Authors: Villarroel H. , Joel N.
Published: December 2006

A modification of the one-axis spindle-stage for the study of the optical indicatrix of crystal grains on the polarizing microscope is described. It allows the crystal to be rotated around axes within a range of about 40° without having to remount it. Some advantages of this variable-axis spindle-stage for obtaining extinction curves and equivibration curves (n0 curves) are illustrated.
Pyroxene and magnetite phenocrysts from the Taupo quaternary rhyolitic pumice deposits, New Zealand
Authors: Ewart A.
Published: December 2006

Chemical 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

Measurements 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

Dalyite, 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

When 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

Specimens 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

Several 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

A 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

Though 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

A 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 spectral reflectivity of synthetic calcium monoferrite
Authors: Phillips R. , Ware N. G.
Published: December 2006

The principal reflectivities of orthorhombic calcium monoferrite have been determined at 500 Å intervals from 4500 to 6500 Å. A small amount of calcium hexaferrite was shown to be present by electron probe examination.
The nature of ‘ameletite’
Authors: Coombs D. S. , Wilkinson J. F. G.
Published: December 2006

Originally 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

The 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

X-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

Group 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

Values 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

A 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

The 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

Parahopeite, 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

Evidence 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

The 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

Oxides 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.
On the composition of natural delafossite
Authors: Hey M. H.
Published: December 2006

Two new microanalyses of delafossite from Nizhniĭ Tagil (the type locality) and Kimberly, Nevada, confirm the accepted formula CuFeO2.
The crystal chemistry of the apatites
Authors: Cockbain A. G.
Published: December 2006

The 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

The 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.
The metallographic structure of the Kodaikanal meteorite
Authors: Axon H. J.
Published: December 2006

From a metallographic study the thermo-mechanical history of Kodaikanal is proposed as a slow structure-forming cool, followed by mechanical damage, then mild reheating, and finally entry to earth.
New stony meteorite finds including two ureilites from the Nullarbor Plain, Western Australia
Authors: McCall G. J. H. , Cleverly W. H.
Published: December 2006

Two 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

New 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.
Homogeneity in alkali feldspars
Authors: Parsons Ian
Published: December 2006

Curves relating spacing, Or content, and structural state of alkali feldspars are reviewed. Discrepancies between the compositions of heated natural perthitic alkali feldspars determined by this method and by chemical analysis are discussed and shown to be largely consistent with incomplete homogenization.
Zoned plagioclase from the charnockites of Kondapalli, Krishna district, Andhra Pradesh, India
Authors: Leelanandam C.
Published: December 2006

Zoning 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

A 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.