An interpretation of the composition of high-silica sericites

1950 ◽  
Vol 29 (211) ◽  
pp. 406-415 ◽  
Author(s):  
Waldemar T. Schaller
Keyword(s):  
Chemical Composition ◽  
Compositional Variation ◽  
Appreciable Quantity ◽  
Divalent Element ◽  
High Silica ◽  
End Members

The high-silica sericites generally contain a corresponding appreciable quantity of a divalent element, usually magnesium, and their chemical composition is interpreted as being intermediate between that of muscovite, KAl2 (AlSi3)O10(OH)2, and that of the equivalent high-silica mica leucophyllite, KAlMg (Si4)O10(OH)2. The series muscovite-leucophyllite includes the named micas phengite (high-silica sericite), mariposite, and alurgite. Selected analyses are plotted and fall on a corresponding straight compositional variation line from muscovite to leucophyllite. It is shown diagrammatically that the analysed sample of mariposite probably contained about 8 % of quartz. It is recommended that the only species names in this series to be retained are those of the end members muscovite and leucophyllite. Their indices of refraction and specific gravities are very similar.

Octahedral occupancy and the chemical composition of diagenetic (low-temperature) chlorites

Clay Minerals ◽  
1991 ◽  
Vol 26 (2) ◽  
pp. 149-168 ◽  
Author(s):  
S. Hillier ◽  
B. Velde
Keyword(s):  
Chemical Composition ◽  
Low Temperature ◽  
Bulk Composition ◽  
Compositional Variation ◽  
Low Grade ◽  
Chemical Analyses ◽  
Method Of Calculation ◽  
Sedimentary Sequences ◽  
Wet Chemical ◽  
Potential Use

AbstractThe chemical composition of about 500 diagenetic chlorites, determined by electron microprobe, has been studied in six different sedimentary sequences spanning conditions from early diagenesis to low-grade metamorphism, in the temperature range 40–330°C. The range of Fe/(Fe + Mg) is almost complete and is positively correlated with Al. Five sequences show the same compositional variation. In each, the most siliceous chlorites have the lowest R2+, substantially more octahedral than tetrahedral Al, and the lowest octahedral totals. Conversely, the least siliceous have the highest R2+, nearly equal octahedral and tetrahedral Al, and octahedral totals close to that for an ideal trioctahedral mineral. A dioctahedral substitution Si[]R2−2 (where [] represents a vacant octahedral site) which decreases with temperature, describes this variation. Low octahedral totals are, however, induced by the method of calculation and need not indicate vacancies; for published wet chemical analyses of metamorphic chlorites they may simply indicate oxidation of Fe. Intergrown dioctahedral phyllosilicates may partly account for apparent vacancies in diagenetic chlorites. Nevertheless, the correlation of composition with temperature and similarities to the temperature-related evolution of synthetic chlorites, suggest that diagenetic chlorites are compositionally distinct from, but metastable with respect to, fully trioctahedral metamorphic chlorites. Temperature-related trends are modified by bulk composition, complicating their potential use for low-temperature geothermometry.

Compositional variation in högbomites from north Connemara, Ireland

1985 ◽  
Vol 49 (354) ◽  
pp. 649-654 ◽  
Author(s):  
N. S. Angus ◽  
R. Middleton
Keyword(s):  
Chemical Composition ◽  
Regional Metamorphism ◽  
The Other ◽  
Partial Substitution ◽  
Compositional Variation ◽  
Physical Parameters ◽  
Chemical Heterogeneity ◽  
High Grade ◽  
Thermal Metamorphism ◽  
Mineral Assemblages

AbstractHögbomite occurs in two contrasting mineral assemblages within the Currywongaun-Dough-ruagh intrusion of north Connemara: a cordierite-rich pelitic xenolith and an orthopyroxenite. In the latter, högbomite and green spinel form blebs within magnetite-ilmenite grains. The högbomite displays significant compositional variation from grain to grain: TiO2 (3.0–6.3%), FeO (21.6–21.3%), MgO (10.0–7.5%), ZnO (3.6–2.4%). This chemical heterogeneity appears to represent variable degrees of partial substitution of Mg and Zn by Ti, in the replacement of spinel by högbomite. By contrast, in the cordierite-hornfels, the högbomite compositions are more notably enriched in iron: TiO2 (4.7–7.0%), FeO (29.6–24.3%), MgO (4.2–6.2%), ZnO (2.7–2.1%). This iron-rich högbomite appears to have formed primarily by interaction between opaque ore and adjacent cordierite, rather than by replacement of spinel.Two high-grade metamorphic episodes appear to be necessary for högbomite growth, one determining chemical composition and the other appropriate physical parameters. In the Connemara occurrences thermal metamorphism and partial melting, coupled with contamination of the surrounding magma, controlled the formation of mineral assemblages rich in Fe, Mg, Al, Ti, and Zn. Emplacement of the intrusion was accompanied by amphibolite facies regional metamorphism and it is to this metamorphic event that the growth of högbomite may be attributed.

scholarly journals Survey on the chemical composition of several tropical wood species

2019 ◽  
Vol 342 ◽  
Author(s):  
Jean Gérard ◽  
Sébastien Paradis ◽  
Bernard Thibaut
Keyword(s):  
Chemical Composition ◽  
Lignin Content ◽  
Silica Content ◽  
Ash Content ◽  
Hot Water ◽  
Mean Values ◽  
High Silica Content ◽  
Distribution Of Values ◽  
High Silica ◽  
Very High

Variability in the chemical composition of 614 species is described in a database containing measurements of wood polymers (cellulose, lignin and pentosan), as well as overall extraneous components (ethanol-benzene, or hot water extracts and ash, with a focus on silica content). These measurements were taken between 1945 and 1990 using the same standard protocol. In all, 1,194 trees belonging to 614 species, 358 genera and 89 families were measured. At species level, variability (quantified by the coefficient of variation) was rather high for density (27%), much lower for lignin and cellulose (14% and 10%) and much higher for ethanol/benzene extractives, hot water extractives and ash content (81%, 60% and 76%). Considering trees with at least five different specimens, and species with at least 10 different trees, it was possible to investigate within-tree and within-species variability. Large differences were found between trees of a given species for extraneous components, and more than one tree should be needed per species. For density, lignin, pentosan and cellulose, the distribution of values was nearly symmetrical, with mean values of 720 kg/m3 for density, 29.1% for lignin, 15.8% for pentosan, and 42.4% for cellulose. There were clear differences between species for lignin content. For extraneous components, the distribution was very dissymmetrical, with a minority of woods rich in this component composing the high value tail. A high value for any extraneous component, even in only one tree, is sufficient to classify the species in respect of that component. Siliceous woods identified by silica bodies in anatomy have a very high silica content and only those species deserve a silica study.

Crystallochemical classifications of phyllosilicates based on the unified system of projection of chemical composition: III. The serpentine-kaolin group

Clay Minerals ◽  
1990 ◽  
Vol 25 (1) ◽  
pp. 93-98 ◽  
Author(s):  
A. Wiewióra
Keyword(s):  
Chemical Composition ◽  
Chemical Systems ◽  
End Members ◽  
Projection Field

AbstractA unified system of projection of chemical composition, prepared initially for micas and chlorites, has been applied to minerals of the serpentine-kaolinite group. It has been shown that the chemical composition in the projection field is controlled by the formula, the unit of which is: (Si(2-x)Alx)O5(OH)4, where u+y+z=3, z=y-x. Using projection fields for different chemical systems it has been shown that among the most important end-members are kaolinite minerals, true serpentines, berthierine, brindleyite, amesite, cronstedtite, greenalite, nepouite and their analogues having different substitutions in the octahedral sheets.

Comparison of Thermal Analysis, Micro Structural and Compositional of Archeological Indigenous Ceramic (Caninhas Site of Canas - SP) with Actual Clay/Ceramic of Region

2010 ◽  
Vol 660-661 ◽  
pp. 1019-1024
Author(s):  
F.P. Nakano ◽  
Simone P. Taguchi ◽  
C.C. Matos ◽  
R.Batista Ribeiro ◽  
Sarinha J.Leone Rosa
Keyword(s):  
Phase Transition ◽  
Thermal Analysis ◽  
Transition Temperature ◽  
Chemical Composition ◽  
Ceramic Material ◽  
Compositional Variation ◽  
Mass Variation ◽  
Hydrated Alumina ◽  
Temperature Decomposition ◽  
Archeological Site

The ceramic material found at the archeological site in Caninhas, shows funerary structures of combustion and various objects of Tupi-Guarani indigenous use. These pieces and fragments were saved and cataloged, in approximately 4000 units. The ceramics present a gradient of color, from ochre to dark gray, when from the surface to the center of the piece, indicating compositional variation caused by inefficient sintering carried out by indigenous people. The goal of this study was to observe the phase transition temperature, decomposition, mass variation and reactions that occur in the archeological and nowadays ceramics (by DSC/TG), together with micro structural analysis (by SEM), phase analysis (by XRD) and chemical composition (by EDS). Ceramics nowadays are sintered with air, in a temperature ranging between 400-800 °C for one hour, and presents heterogeneous microstructure. The archeological ceramics were identified by the ilitte, hydrated alumina, lutecite and quartz phase, and the caulinite, lutecite and quartz phase in clay produced today from that region differs in all characteristics and aspects according to time. The interaction between different areas of expertise is fundamental to aggregate knowledge: the use of ceramic material engineering to archeological application.

Three compositional varieties of perovskite from kimberlites of the Lac de Gras field (Northwest Territories, Canada)

2001 ◽  
Vol 65 (1) ◽  
pp. 133-148 ◽  
Author(s):  
A. R. Chakhmouradian ◽  
R. H. Mitchell
Keyword(s):  
High Pressures ◽  
Compositional Variation ◽  
Type I ◽  
Evolutionary Trend ◽  
Type Ii ◽  
Type Iii ◽  
Composition I ◽  
End Members ◽  
Textural Evidence ◽  
Kimberlite Field

AbstractIn hypabyssal and crater-facies kimberlites of the Lac de Gras kimberlite field, perovskite occurs as reaction-induced rims on earlier-crystallized Ti-bearing minerals (magnesian ilmenite and priderite), inclusions in atoll spinels and discrete crystals in a serpentine-calcite mesostasis. The mineral is associated with spinels, apatite, monticellite, phlogopite, baryte, Fe-Ni sulphides, ilmenite, diopside and zircon. Uncommon accessory phases found in an assemblage with perovskite include titanite, monazite- (Ce), witherite, strontium-apatite, khibinskite, djerfisherite, wollastonite, pectolite, suolunite, hydroxyapophyllite and bultfonteinite. Three types of perovskite can be distinguished on the basis of composition: (I) REE-Nb-Al-poor perovskite with relatively high Sr and K contents (up to 2.2 and 0.6 wt.% oxides, respectively) occurring as mantles on priderite and inclusions in atoll spinels; (II) perovskite with elevated Al, Fe, Nb and LREE (up to 1.4, 8.3, 9.1 and 17.0 wt.% oxides, respectively) found as discrete crystals and rims on macrocrystic ilmenite; (III) perovskite significantly enriched in Na, Sr, Nb and LREE (up to 3.3, 3.4, 13.0 and 22.6 wt.% oxides, respectively) found as rims on perovskite I and II. The overwhelming majority of perovskite is represented by discrete crystals of type II. In some occurrences, this type of perovskite also has high Th contents (up to 5.5 wt.% ThO2) and Zr contents (up to 3.7 wt.% ZrO2). Textural evidence indicates that perovskite shows an overall evolutionary trend from the most primitive type I towards type III showing the highest Na, Nb and LREE contents. Perovskite of type I probably crystallized under relatively high pressures prior to the precipitation of MUM spinels. Perovskite II crystallized after magnesiochromite, pleonaste and MUM (magnesian ulvöspinel-magnetite) spinels, under increasing fO2. The most compositionally evolved type III formed during near-solidus re-equilibration of the earlier-crystallized perovskite. The compositional variation of the Lac de Gras perovskite can be adequately characterized in terms of five major end-members: CaTiO3 (perovskite), CeFeO3, NaNbO3 (lueshite), Na0.5LREE0.5TiO3 (loparite), and CaFe0.5Nb0.5O3 (latrappite).

scholarly journals Ontology, archetypes and the definition of ‘mineral species’

2021 ◽  
Vol 85 (2) ◽  
pp. 125-131
Author(s):  
Frank C. Hawthorne ◽  
Stuart J. Mills ◽  
Frédéric Hatert ◽  
Mike S. Rumsey
Keyword(s):  
Chemical Composition ◽  
Specific Property ◽  
Intrinsic Property ◽  
Mineral Species ◽  
General Definition ◽  
Intrinsic Properties ◽  
Space Group ◽  
Bond Topology ◽  
Definition Of ◽  
End Members

AbstractOntology deals with questions concerning what things exist, and how such things may be associated according to similarities and differences and related within a hierarchy. Ontology provides a rigorous way to develop a general definition of a mineral species. Properties may be divided into two principal groups: an intrinsic property is characteristic of the object and is independent of anything else; an extrinsic property depends on the relation between the object and other things. A universal is an entity that is common to all objects in a set. Here the objects are mineral samples, each entity is a specific property of these minerals, and the set of objects is all mineral samples of that mineral species. The key intrinsic properties of a mineral species are its name, its end-member formula and Z (the number of formula units in the unit cell), its space group and the bond topology of the end-member structure. These are also universals as they are common to all mineral samples belonging to that mineral species. An archetype is a pure form which embodies the fundamental characteristics of an object. Thus the archetype of a mineral species embodies the above set of universals. Real mineral samples of this mineral species are imperfect copies of that archetype, with a range of chemical composition defined by the boundaries between end-member formulae of this and other end members of the same bond topology. The result is a formal definition of a mineral species: A specific mineral species is the set of imperfect copies of the corresponding archetype and is defined by the following set of universals: name, end-member formula and Z, space group, and bond topology of the end-member structure, with the range of chemical composition limited by the compositional boundaries between end members with the same bond topology.

Minerals of the rhabdophane group and the alunite supergroup in microgranite: products of low-temperature alteration in a highly acidic environment from the Velence Hills, Hungary

2018 ◽  
Vol 82 (6) ◽  
pp. 1277-1300 ◽  
Author(s):  
Martin Ondrejka ◽  
Peter Bačík ◽  
Tomáš Sobocký ◽  
Pavel Uher ◽  
Radek Škoda ◽  
...  
Keyword(s):  
Low Temperature ◽  
Mineral Assemblage ◽  
Electron Probe ◽  
Compositional Variation ◽  
Acidic Environment ◽  
Sulfide Mineralization ◽  
Sulfate Solutions ◽  
Substitution Mechanism ◽  
Compositional Variations ◽  
End Members

ABSTRACTAn assemblage of alunite-supergroup minerals (ASM), rhabdophane-group minerals (RGM), goethite and associated clay minerals occurs in Permian A-type porphyritic microgranite in the eastern part of the Velence Hills, Hungary. The secondary sulfates/phosphates include jarosite, Pb-rich jarosite and alunite, corkite, hinsdalite and rhabdophane-(Ce), -(La) and -(Nd). Detailed electron probe microanalysis and Raman spectroscopy reveal a wide miscibility among RGM end-members and show a rhabdophane–tristramite–brockite solid solution with extensive compositional variation. Moreover, ASM show heterogeneous composition and complex substitution mechanisms within the alunite, beudantite and plumbogummite groups. The formation of this rare mineral assemblage reveals extensive remobilization of rare-earth elements (REE), Th, U, P, S, Fe and Pb under supergene conditions. Compositional variations and substitution trends of the RGM investigated indicate that Th, U, Ca and Pb are incorporated into the rhabdophane structure by a (Ca, Pb)2+ + (Th, U)4+ ↔ 2REE3+ substitution mechanism. Consequently, we suggest the following end-member formulae for RGM containing divalent and tetravalent cations: (Ca0.5Th0.5)PO4·H2O for brockite, (Pb0.5Th0.5)PO4·H2O for grayite and (Ca0.5U0.5)PO4·2H2O for tristramite. The ASM and RGM originated from total leaching of the primary magmatic REE, Th, U and P minerals in the microgranite [most probably allanite-(Ce), fluorapatite and possibly also xenotime-(Y)], together with input of Pb and S in low-temperature, acid sulfate solutions, connected with an adjacent Palaeogene andesite–diorite intrusion and the accompanying hydrothermal sulfide mineralization.

The Principle of Constituent Analysis, with Special Reference to the Calculation of Weight Percentages of Minerals in Metamorphic Rocks

1973 ◽  
Vol 10 (5) ◽  
pp. 657-669 ◽  
Author(s):  
Tsu-Min Fuh
Keyword(s):  
Chemical Composition ◽  
Metamorphic Rock ◽  
Dimensional Space ◽  
Metamorphic Rocks ◽  
Chemical Compositions ◽  
Bulk Chemical Composition ◽  
Orthogonal Axis ◽  
Bulk Chemical ◽  
Axis I ◽  
End Members

The principle of constituent analysis is introduced. Assuming that a component (end member) consists of n variables in percentage form and that m different components (m ≤ n) constitute each of N samples, the samples can be treated as N points in m-dimensional space. Points represented by m end members are characterized by being non-coplanar and non-collinear in m-dimensional space. The amount of the mth end member contained in a sample is calculated as Xm−1i/Xm−1 m, where Xm−1 is the length of (m−1)th orthogonal axis; i and m in subscript Xm−1 are for the sample and mth end member, respectively; and the end members are successively put on the origin of the coordinate, X1, X1−X2, X1−X2−X3,…, and X1−X2 …−Xm−1 axes.In a metamorphic rock, m points are equivalent to constituent minerals. If the chemical compositions of constituent minerals and the bulk chemical composition of the rock are known, the method outlined in this paper provides information on equilibrium assemblages and allows computation of the amounts of constituent minerals.

Causes of compositional diversity in a lobe of the Half Dome granodiorite, Tuolumne Batholith, Central Sierra Nevada, California

2009 ◽  
Vol 100 (1-2) ◽  
pp. 173-183 ◽  
Author(s):  
R. C. Economos ◽  
V. Memeti ◽  
S. R. Paterson ◽  
J. S. Miller ◽  
S. Erdmann ◽  
...  
Keyword(s):  
Sierra Nevada ◽  
Magma Mixing ◽  
Minimum Size ◽  
Compositional Variation ◽  
Isotopic Study ◽  
High Silica ◽  
Dominant Process ◽  
Compositional Diversity ◽  
Compatible Elements ◽  
Host Rocks

ABSTRACTThe causes of compositional diversity in the Tuolumne Batholith, whether source heterogeneity, magma mixing, or fractional crystallisation, is a matter of longstanding debate. This paper presents data from detailed mapping and a microstructural and major element, trace element and isotopic study of an elongate lobe of the Half Dome granodiorite that protrudes from the southern end of the batholith. The lobe is normally zoned from quartz diorite along the outer margin to high-silica leucogranite in the core. Contacts are steep and gradational, except for the central leucogranite contact, which is locally sharp: magmatic fabrics overprint contacts. A striking feature of the lobe is the 18 wt SiO2 range comparable to that observed for the entire Tuolumne Batholith. Feldspar-compatible elements (Sr and Ba) decrease towards the centre, while Rb increases. Light and middle REEs show a smooth decrease towards the centre of the lobe. Calculated initial isotopic ratios of 87Sr/86Sr(i) and εNd(t) have identical values within error across the lobe, except in the central leucogranite, the most silica rich phase, which shows a slightly more crustal signature. Field, structural, geochemical and isotopic data suggest that fractionation was the dominant process causing compositional variation in this lobe. It is envisioned that this fractionation/crystal sorting occurred in a vertically flowing and evolving magma column with the present map pattern representing a cross-section of this column. Thus the areal extent of the lobe represents a minimum size of interconnected melt at the emplacement level of the Tuolumne Batholith and, given its marginal position, limited width and proximity to colder host rocks, implies that fractionation in larger chambers likely occurred in the main Tuolumne Batholith magma chamber(s).

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