Mineralogical Magazine
SCOPUS (1969-1970,1978-1989,1993-2023)SCIE-ISI
0026-461X
1471-8022
Anh Quốc
Cơ quản chủ quản: Mineralogical Society , MINERALOGICAL SOC
Lĩnh vực:
Geochemistry and Petrology
Các bài báo tiêu biểu
Nomenclature of Amphiboles; Report of the Subcommittee on Amphiboles of the International Mineralogical Association Commission on New Minerals and Mineral NamesAbstract The International Mineralogical Association's approved amphibole nomenclature has been revised in order to simplify it, make it more consistent with divisions generally at 50%, define prefixes and modifiers more precisely and include new amphibole species discovered and named since 1978, when the previous scheme was approved. The same reference axes form the basis of the new scheme and most names are little changed but compound species names like tremolitic hornblende (now magnesiohornblende) are abolished and also crossite (now glaucophane or ferroglaucophane or magnesioriebeckite or riebeckite), tirodite (now manganocummingtonite) and dannemorite (now manganogrunerite). The 50% rule has been broken only to retain tremolite and actinolite as in the 1978 scheme so the sodic calcic amphibole range has therefore been expanded. Alkali amphiboles are now sodic amphiboles. The use of hyphens is defined. New amphibole names approved since 1978 include nyböite, leakeite, kornite, ungarettiite, sadanagaite and cannilloite. All abandoned names are listed. The formulae and source of the amphibole end member names are listed and procedures outlined to calculate Fe3+ and Fe2+ when not determined by analysis.
Tập 61 Số 405 - Trang 295-310 - 1997
A general equation for estimating Fe3+ concentrations in ferromagnesian silicates and oxides from microprobe analyses, using stoichiometric criteriaAbstract A simple general equation is presented for estimating the Fe3+ concentrations in ferromagnesian oxide and silicate minerals from microprobe analyses. The equation has been derived using stoichiometric criteria assuming that iron is the only element present with variable valency and that oxygen is the only anion. In general, the number of Fe3+ ions per X oxygens in the mineral formula, F , is given by; where T is the ideal number of cations per formula unit, and S is the observed cation total per X oxygens calculated assuming all iron to be Fe2+ . Minerals for which this equation is appropriate include pyralspite and ugrandite garnet, aluminate spinel, magnetite, pyroxene, sapphirine and ilmenite. The equation cannot be used for minerals with cation vacancies (e.g. micas, maghemite) unless, as in the case of amphiboles, the number of ions of a subset of elements in the formula can be fixed. Variants of the above equation are presented for some of the numerous published schemes for the recalculation of amphibole formulae. The equation is also inappropriate for minerals showing Si4+ = 4H+ substitution (e.g. staurolite, hydrogarnet), minerals containing an unknown proportion of an unanalysed element other than oxygen (e.g. boron-bearing kornerupine) and minerals containing two or more elements with variable valency.
Tập 51 Số 361 - Trang 431-435 - 1987
Unit cell refinement from powder diffraction data: the use of regression diagnosticsAbstract We discuss the use of regression diagnostics combined with nonlinear least-squares to refine cell parameters from powder diffraction data, presenting a method which minimizes residuals in the experimentally-determined quantity (usually 2θhkl Ehkl ). Regression diagnostics, particularly deletion diagnostics, are invaluable in detection of outliers and influential data which could be deleterious to the regressed results. The usual practice of simple inspection of calculated residuals alone often fails to detect the seriously deleterious outliers in a dataset, because bare residuals provide no information on the leverage (sensitivity) of the datum concerned. The regression diagnostics which predict the change expected in each cell constant upon deletion of each observation (hkl reflection) are particularly valuable in assessing the sensitivity of the calculated results to individual reflections. A new computer program, implementing nonlinear regression methods and providing the diagnostic output, is described.
Tập 61 Số 404 - Trang 65-77 - 1997
Mineral replacement reactions: from macroscopic observations to microscopic mechanismsAbstract Mineral replacement reactions take place primarily by dissolution-reprecipitation processes. Processes such as cation exchange, chemical weathering, deuteric alteration, leaching, pseudomorphism, metasomatism, diagenesis and metamorphism are all linked by common features in which one mineral or mineral assemblage is replaced by a more stable assemblage. The aim of this paper is to review some of these aspects of mineral replacement and to demonstrate the textural features they have in common, in order to emphasize the similarities in the underlying microscopic mechanisms. The role of volume change and evolution of porosity is explored both from natural microtextures and new experiments on model replacement reactions in simple salts. It is shown that the development of porosity is often a consequence of mineral replacement processes, irrespective of the relative molar volumes of parent and product solid phases. The key issue is the relative solubility of the phases in the fluid phase. Concepts such as coupled dissolution-precipitation, and autocatalysis are important in understanding these processes. Some consequences of porosity generation for metamorphic fluid flow as well as subsequent crystal growth are also discussed.
Tập 66 Số 5 - Trang 689-708 - 2002
Chemistry of chromian spinel in volcanic rocks as a potential guide to magma chemistryAbstract Chromian spinel in volcanic rocks is a potential discriminant for magma chemistry. The TiO2 content of spinel, compared at similar Fe3+ /(Cr + Al + Fe3+ ) ratios, can distinguish island arc basalts from intraplate basalts. MORB spinels are low in this ratio and are intermediate for the TiO2 level at comparable Fe3+ ratios. Spinels from back-arc basin basalts, although similar in TiO2 /Fe3+ ratio, are more enriched in Fe3+ than the MORB spinels. Spinels in the oceanic plateau basalts are distinctly lower in TiO2 than other intraplate basalt spinels and even slightly lower in TiO2 than the MORB spinels. The data were successfully applied to estimate the kind of the magma from which spinelbearing cumulates, especially dunites, were formed. Original magma chemistry of altered or metamorphosed volcanics in which spinels survive can also be estimated by the chemistry of relict spinel alone. It is possible to estimate the magma type of source volcanics for detrital spinel particles of volcanic derivation.
Tập 56 Số 383 - Trang 173-184 - 1992
Crystal structures of some double hydroxide mineralsSummary
Three groups of minerals are discussed,
which are typified by pyroaurite and sjögrenitc,
hydrocalumite, and ettringite. All show
interesting structural features. In the
pyroaurite-sjögrenite group, brucite-likc layers
carrying a net positive charge alternate with
layers in which the oxygen atoms of carbonate
groups and water molecules are statistically
distributed on a single set of sites; other anions
may replace the carbonate, especially in synthetic
phases. Hydrocalumite and related synthetic phases
also have layer structures in which positively
charged main layers alternate with intermediate
layers containing anions and water molecules; the
anions occur in cavities and their nature can
again vary widely. In the ettringite group, the
structures are based on positively charged
columns, between which occur channels containing
anions and sometimes also water molecules. This
group includes thaumasite, the only natural
mineral known to contain silicon six-coordinated
by oxygen that is not a high-pressure phase. The
thermal dehydration behaviour in each group is
briefly considered.
Tập 39 Số 304 - Trang 377-389 - 1973
Atomic number and crystallographic contrast images with the SEM: a review of backscattered electron techniquesAbstract Backscattered electrons (BSE) are incident electrons reflected back from a target specimen and imaged with the scanning electron microscope (SEM). Three distinct BSE signals exist: atomic number or Z-contrast, in which composition determines image contrast; orientation contrast, in which specimen crystal structure determines image contrast; and electron channelling patterns (ECP), which are unique for a particular crystal orientation. The origins of these three signals are described, with particular attention being given to the necessary SEM operational and specimen preparation requirements. Z-contrast images are relatively simple to obtain and also have a familiar appearance such that their usage should become commonplace. ECP in comparison require subsequent interpretation which depends on the crystal structure and the relationship between crystal and specimen coordinate systems. A general solution to ECP interpretation is therefore presented, involving the construction of reference ‘ECP-maps’ over the surface of a sphere. A brief summary of the applications and potential use of the three BSE signals in the geological sciences is also given.
Tập 51 Số 359 - Trang 3-19 - 1987
The catalysis of mineral reactions by water and restrictions on the presence of aqueous fluid during metamorphismAbstract The problems of characterizing inter-granular regions and of estimating rates of intergranular diffusion in metamorphic rocks are discussed. Inter-granular regions can be anhydrous, hydrated but under-saturated with H2 O, or saturated with H2 O, but only in the latter case can a free aqueous fluid phase be present. Estimates of intergranular diffusion coefficients (D IGR ) at 550°C derived from a variety of published experimental work, vary from ∼ 10−8 m2 s−1 for diffusion of species through an intergranular fluid film to ⩽ 4 × 10−24 m2 s−1 for diffusion of SiO2 or O in anhydrous grain boundaries in quartzite. Estimates ofD IGR for hydrated grain boundaries vary from ∼ 10−13 m2 s−1 to ∼ 10−21 m2 s−1 ; the concentration of H2 O in the grain boundaries and the identity of the diffusing species (generally unknown) may be important controlling factors, and there exists the possibility of a spectrum of values between these two extremes. Using available kinetic data it is shown that a free aqueous fluid could never have been present in parts of the basement terrane of the Sesia Zone (Western Alps) during uplift from the eclogite facies, except possibly late in the cooling history. The breakdown of sodic pyroxene + quartz occurred in response to the localized infiltration of catalytic aqueous fluid, possibly over a time interval as short as 6–6000 a, and possibly under conditions remote from equilibrium. H2 O-present conditions during a dehydration reaction in metapelites of the Adula nappe (central Alps) could also have been of short duration. These examples are consistent with a model in which basement rocks at deep crustal levels are dry for long periods of time and in which the development of equilibrium mineral assemblages and microstructures generally occurs over relatively short periods of time under transitory fluid-present conditions (caused by devolatilization and/or infiltration).
Tập 50 Số 357 - Trang 399-415 - 1986
Diamond formation in the deep mantle: the record of mineral inclusions and their distribution in relation to mantle dehydration zonesAbstract Studies of the inclusions contained in natural diamonds have shown the occurrence of minerals which must have formed at depths below the lithosphere and which may be closely matched with the silicate mineral assemblages determined by high pressure and temperature experimental studies for depths of 300 to 800 km in the Earth's mantle. The inclusions come principally from two main depth zones: (1) the lower asthenosphere and upper transition zone; (2) the Upper Mantle/Lower Mantle (UM/LM) boundary region and the uppermost LM. The inclusions from zone 1 are very largely majoritic garnets (with or without clinopyroxene) which indicate bulk compositions of eclogitic/metabasic affinity. The minerals from zone 2 include Ca-Si and Mg-Si perovskites and ferropericlase and are dominantly of metaperidotitic bulk composition, but include some possible metabasite assemblages. In many of these natural assemblages, the tetragonal almandine pyrope phase occurs rather than the garnet found in experiments. As natural diamonds are believed to crystallize in fluids/melts, the hypothesis is developed that the restriction of diamonds and inclusions of particular compositions to the above two depth intervals is because they are controlled by loci of fluid/melt occurrence. Attention is focused on subduction zones because both suites of inclusions show some evidence of subducted protoliths. The lower zone (600–800 km) coincides with the region where dehydration may be expected for hydrous ringwoodite and dense hydrous Mg-silicates formed in subducted peridotites. The dehydration of lawsonite in subducted metabasites provides a particular location for melt formation and the inclusion of the shallower (~ 300 km) majoritic inclusions. For the deeper majoritic inclusions in the region of the upper transition zone, melt development may occur as a consequence of the hydrous wadsleyite-to-olivine transformation, and such melt may then interact with the upper crustal portion of a subducting slab. These suggestions offer an explanation of the depth restrictions and the compositional restrictions of the inclusions. The differences in δ13 C values in the host diamonds for the two suites of inclusions may also be explained on this basis.
Tập 74 Số 2 - Trang 189-215 - 2010
Arsenic hazard in shallow Cambodian groundwatersAbstract Our recent discovery of hazardous concentrations of arsenic in shallow sedimentary aquifers in Cambodia raises the spectre of future deleterious health impacts on a population that, particularly in non-urban areas, extensively use untreated groundwater as a source of drinking water and, in some instances, as irrigation water. We present here small-scale hazard maps for arsenic in shallow Cambodian groundwaters based on >1000 groundwater samples analysed in the Manchester Analytical Geochemistry Unit and elsewhere. Key indicators for hazardous concentrations of arsenic in Cambodian groundwaters include: (1) well depths greater than 16 m; (2) Holocene host sediments; and (3) proximity to major modern channels of the Mekong (and its distributary the Bassac). However, high-arsenic well waters are also commonly found in wells not exhibiting these key characteristics, notably in some shallower Holocene wells, and in wells drilled into older Quaternary and Neogene sediments. It is emphasized that the maps and tables presented are most useful for identifying current regional trends in groundwater arsenic hazard and that their use for predicting arsenic concentrations in individual wells, for example for the purposes of well switching, is not recommended, particularly because of the lack of sufficient data (especially at depths >80 m) and because, as in Bangladesh and West Bengal, there is considerable heterogeneity of groundwater arsenic concentrations on a scale of metres to hundreds of metres. We have insufficient data at this time to determine unequivocally whether or not arsenic concentrations are increasing in shallow Cambodian groundwaters as a result of groundwater-abstraction activities.
Tập 69 Số 5 - Trang 807-823 - 2005