Chemistry of biotites from a zoned granitic pluton in Morocco

1983 ◽  
Vol 47 (344) ◽  
pp. 365-369 ◽  
Author(s):  
A. Mahmood
Keyword(s):  
Chemical Analyses ◽  
Granitic Pluton ◽  
Structural Formulae ◽  
Host Rocks

AbstractChemical analyses and structural formulae of biotites from the Zaër pluton, a zoned granitic body in the Central Hercynian Massif of Morocco, are presented. The pluton grades from more mafic single-mica granodioritic facies near the margin to more felsic two-mica granitic facies in the central part. There is a relationship between the composition of the biotites and that of the host rocks. Biotite composition in the internal two-mica facies was influenced by a hydrothermal phase.

Ultrabasic eruptives with alnöitic-kimberlitic affinities from Malaita, Solomon Islands

1965 ◽  
Vol 34 (268) ◽  
pp. 16-34 ◽  
Author(s):  
J. B. Allen ◽  
T. Deans
Keyword(s):  
Solomon Islands ◽  
Chemical Analyses ◽  
Alkaline Rocks ◽  
Kimberlite Indicator Minerals ◽  
Host Rocks ◽  
Indicator Minerals

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

Changes in phlogopites during their artificial alteration

Clay Minerals ◽  
1967 ◽  
Vol 7 (2) ◽  
pp. 215-227 ◽  
Author(s):  
A. C. D. Newman
Keyword(s):  
Negative Charge ◽  
Hydroxyl Groups ◽  
Vibration Band ◽  
Chemical Analyses ◽  
Water Of Hydration ◽  
Angular Vibration ◽  
Oxygen Anions ◽  
Structural Formulae ◽  
Sodium Tetraphenylboron ◽  
Silicate Layers

AbstractWhen phlogopites containing only a little iron are artificially altered with sodium tetraphenylboron solutions, the vermiculite-like products contain fewer interlayer cations than the original micas. Structural formulae of the products are calculated from the chemical analyses, together with infrared examination of the angular vibration band of water at 1650 cm−1 to distinguish between water of hydration and hydroxyl groups. The formulae obtained are consistent with the weight-loss curves and show that the products contain, more than 4(OH,F) per formula unit. The interpretation of these formulae is that the silicate layers lose net negative charge by protonation of structural oxygen anions to form new hydroxyl groups.

A chondrodite–humite-spinel marble from Sørfinnset,near Glomfjord, northern Norway

1964 ◽  
Vol 33 (267) ◽  
pp. 1066-1080 ◽  
Author(s):  
R. Beadshaw ◽  
B. E. Leake
Keyword(s):  
Modal Analysis ◽  
Previous Analysis ◽  
Chemical Analyses ◽  
Northern Norway ◽  
X Ray ◽  
Structural Work ◽  
Structural Formulae ◽  
Ti Substitution

SummaryA chemical and modal analysis of the marble, together with chemical analyses of the coexisting spinel and the chondrodite-humite mixture are given. The spinel, a 8·101 ± 0·001 Å, n 1·731 ± 0·003, is much richer in iron (Niggli's mg 0·90), than the humite mixture (mg 0·99), which agrees with the only previous analysis of a coexisting spinel and humite mineral. It was not possible to separate the two humite minerals from each other and analyse them, but the analysis of the mixture shows less iron than any previously analysed chondrodite or humite; the composition is very near to that of humite although the mixture contains at least 50 % chondrodite. It is pointed out that there are serious discrepancies between the chemical analyses of some of the humite minerals and their accepted structural formulae. The possibility that some humite minerals contain irregular numbers of olivine and Mg(OH,F)2-TiO2 layers would fit the available chemical analyses of the humite minerals very well but more structural work is needed as the present scanty X-ray results do not confirm this view. It is suggested that Ti substitution in the humite minerals is primarily controlled by the availability of F in the rock.

scholarly journals Metasomatic zonation of an ultramafic lens at Ikátoq, near Færingehavn, southern West Greenland

1980 ◽  
Vol 135 ◽  
pp. 1-32
Author(s):  
M.R Sharpe
Keyword(s):  
Carbonate Rock ◽  
The Body ◽  
Chemical Analyses ◽  
Ion Migration ◽  
West Greenland ◽  
Mineral Reaction ◽  
Parent Rocks ◽  
Reaction Stoichiometry ◽  
Common Parent ◽  
Host Rocks

The Ikátoq zoned ultramafic lens occurs as an elliptical body in Archaean gneisses and amphibolites to the south of Færingehavn, southern West Greenland. From the unaltered serpentinite core to the contact with the surrounding gneisses five zones were distinguished: serpentinite (5), talc-carbonate rock (4), tale (3), amphibole (2) and chlorite (1): their interrelationships are discussed in the light of the theory of zoning. It is shown that these five main lithological types developed from a common parent rock under the inf1uence of low temperature metamorphism as a process of steatisation – the outer chlorite zone representing altered host rocks, whilst the inner tale, tale-carbonate and serpentinite shells represent changed serpentine core. The original junction between the two parent rocks lies in the amphibole zone. The growth process of the zones is discussed and evidence concerning these mechanisms is presented. Estimates of bulk transport and ion migration during the alteration are developed from the chemical analyses, based on whole-rock formulas and equivalent volumes, using ideal-mineral reaction stoichiometry. The system was open to migrating components, and it is shown that the body lost Mg to the gneisses, which in turn supplied some Ca and K to the reacting system. It is likely that CO2 and H2O were permanently in excess. A volume contraction of approximately 6 per cent during the steatisation process is postulated.

Garnets from the Upper Swat Hornblendic Group, Swat District, Pakistan. Part I: Garnets from gneisses and pegmatites

1975 ◽  
Vol 40 (309) ◽  
pp. 53-58 ◽  
Author(s):  
Zulfiqar Ahmed ◽  
Shafeeq Ahmed
Keyword(s):  
Refractive Index ◽  
Relative Abundance ◽  
Chemical Analyses ◽  
Host Rocks

SummaryChemical analyses of eleven garnets from orthogneisses and related pegmatites, belonging to the Upper Swat Hornblendic Group, Pakistan, are presented along with the petrographic descriptions of the host rocks. The garnets show dominant almandine content, followed by grossular pyrope, spessartine, and andradite, in order of relative abundance. One garnet sample is different from the rest in having higher andradite and spessartine contents and higher refractive index, and is also different in habit. This is the first detailed study of garnets from Pakistan.

Axinites from the contact skarns of the Meldon aplite, Devonshire, England

1969 ◽  
Vol 37 (285) ◽  
pp. 45-48 ◽  
Author(s):  
M. Nawaz Chaudhry ◽  
R. A. Howie
Keyword(s):  
Optical Properties ◽  
Refractive Indices ◽  
Chemical Analyses ◽  
Linear Variation ◽  
Variation Diagram ◽  
Host Rocks ◽  
Iron And Manganese

SummaryChemical analyses, optical properties, and specific gravities are presented for nine axinites. A reciprocal substitution relationship is demonstrated between Mg and Mn2+, and a linear variation diagram is constructed between refractive indices and the (Fe2++Fe3++Mn2++Ti) ions calculated on the basis of 16(O,OH). The composition of these axinites is independent of the composition of their host rocks; their colour appears to be independent of the Fe2+/Mn2+ ratio for the range of iron and manganese values of the specimens investigated.

Hydrous micas

1952 ◽  
Vol 29 (218) ◽  
pp. 929-932 ◽  
Author(s):  
George Brown ◽  
Keith Norrish
Keyword(s):  
Chemical Analysis ◽  
Structural Unit ◽  
Adsorbed Water ◽  
Structural Formula ◽  
Hydroxyl Groups ◽  
Chemical Analyses ◽  
Total Oxygen ◽  
Structural Water ◽  
Fine Grained ◽  
Structural Formulae

Hydrous micas differ from normal micas in that they contain less potassium and more water. In the calculation of structural formulae from their chemical analyses, two methods have been used which rely on the following different assumptions:1. As these minerals are often fine-grained and may contain adsorbed water, no reliance is placed on the value of H2O+ (water lost above 105° C.) as a measure of structural water. The water content is ignored and the structural formula is calculated on the basis of 20 oxygens plus 4 hydroxyls per structural unit. This method has been used by Hendricks and Ross and by Grim and Bradley.2. The water which is recorded as H2O+ in the chemical analysis is assumed to represent hydroxyl groups in the aluminosilicate layers of the minerals. Thus, instead of having 20 oxygens and 4 hydroxyl ions per structural unit as in normal micas, formulae are derived which show less than 20 oxygens and more than 4 hydroxyls, the total oxygen plus hydroxyl remaining 24. This method has been used by Brammall, Leech, and Bannister.

scholarly journals Geology and genesis of vein-type corundum deposits in the Hafafit-Nugrus area, South Eastern Desert, Egypt

Geologos ◽  
2020 ◽  
Vol 26 (3) ◽  
pp. 181-197
Author(s):  
Soliman Abu Elatta A. Mahmoud ◽  
Hani H. Ali
Keyword(s):  
Eastern Desert ◽  
Ultramafic Rocks ◽  
Field Observations ◽  
Chemical Analyses ◽  
South Eastern ◽  
Ophiolitic Mélange ◽  
Vein Type ◽  
Different Ages ◽  
Host Rocks

Abstract Unusual deposits formed by corundum are described from two separate pegmatitic veins in the Hafafit-Nugrus area of the South Eastern Desert of Egypt. Other related minerals are described too. The vein-type of corundum at Locality 1 (Vein 1) crosscuts through exposed rocks of an ophiolitic mélange, whereas at Locality 2 (Vein 2), it crosscuts through exposed serpentinised ultramafic rocks. The main minerals in Vein 1 are plagioclase, corundum, grossular, phlogopite, muscovite and clinochlore, while almandine, xenotime-(Y), allanite-(Ce), zircon, Cr-rich spinel, apatite, titanite, fergusonite-(Y), meta-ankoleite, U-rich thorite (uranothorite), carbonate and illite are the accessories. In Vein 2, the main minerals are plagioclase, corundum, phlogopite and chlorite, while clinochlore, euxenite-(Y), Nb-rich rutile, almandine, xenotime-(Y), allanite-(Ce), zircon, spinel, apatite, titanite, kasolite, dickite, illite, carbonate, antigorite and talc are accessories. The two types of corundum veins differ in their concentrations of Th, U, Zr, Nb, Ta, REE, Y and Li in whole-rock compositions. Field observations, mineralogy and chemical analyses of samples from the two veins of corundum deposits, as well as concentrations of chromophore elements in corundum crystals, suggest metasomatic origins. The present study suggests that the two types of corundum veins formed at different ages from different residual magmas that underwent in-situ hybridisation with the host rocks.

The paragenesis of garnet in charnockite, enderbite, and related granulites

1957 ◽  
Vol 31 (238) ◽  
pp. 565-586 ◽  
Author(s):  
R. A. Howie ◽  
A. P. Subramaniam
Keyword(s):  
Mineral Assemblage ◽  
Chemical Analyses ◽  
Type Area ◽  
Host Rocks ◽  
Bulk Chemistry

SummaryThe presence of garnet in acid rocks of the charnockite series south of Madras is reported. Petrographic deseriptions of garnetiferous enderbites and related pyroxene-granulites, khondalites, and leptynites are accompanied by new chemical analyses of 6 rocks, 8 garnets, and 5 orthopyroxenes from the type area near Madras, and from Ceylon, Varberg, and Uganda. The garnets show a considerably higher FeO/MgO ratio than the coexisting ortbopyroxenes and the host rocks. The presence or absence of garnet appears to be related to the bulk chemistry of the rocks. Basic garnetiferous granulites associated with these rocks are considered to represent an unstable mineral assemblage and may be genetically unrelated to the acid types. Attention is drawn to the prevalence of enderbitic rocks in the type area.

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