Quantitative Mineralogical Analysis Research Articles

Changes in mineralogy of loess–paleosol sections across the Chinese Loess Plateau

Quantitative mineralogical analysis of bulk samples and single particles was carried out on three loess sections of different local climate settings on the Chinese Loess Plateau (CLP). Mineralogy, geochemistry, and single-particle petrography of loess and paleosols are relatively uniform over the CLP. However, in detail, there are mineralogical changes related to eolian process and chemical weathering. Particle-size sorting eastward from western sources led to an eastward increase of the total phyllosilicate contents enriched in fine illitic clay minerals. After deposition, detrital minerals susceptible to chemical weathering were sequentially altered in a progressive fashion with increasing precipitation in the order of calcite, dolomite, biotite, illite, chlorite, amphibole, and plagioclase. The weathering of biotite, chlorite, and illite resulted in a significant increase of expandable phyllosilicate contents. The sequential weathering of the minerals is reflected chemically in the decrease of Na and Mg and the increase of iron oxidation. Mineralogy of the Chinese loess at individual sites reflects the effects of size fractionation during eolian transportation and progressive sequential weathering along the climatic gradient, and it is essential to consider both effects when using mineralogical and dependent chemical data in the paleoclimatic reconstruction of the CLP.

Assessing potassium reserves in northern temperate grassland soils: A perspective based on quantitative mineralogical analysis and aqua-regia extractable potassium

Increasing demand for locally produced farm products, with a lower input of mineral fertilisers, leads to a greater reliance on the inherent capacity of soils to supply plant nutrients. Typically 98% of all soil potassium (K) is found in K-feldspars and phyllosilicates, however the potential bioavailability of K from different mineral forms varies significantly. As a basis for improving sustainable nutrient management options for grassland systems we set out to determine 1) how soil parent material influences the amount of K in soils, 2) how the K is quantitatively distributed between mineral groups, 3) relationships between quantitative mineralogy (X-ray powder diffraction (XRPD)), total K (X-ray fluorescence) and the more widely available measurement of aqua-regia extractable K, and (4) how the studied soils could be ranked in terms of their long-term potential capacity to deliver K to plants. Soils representing eight of the most extensive soil associations (defined by different parent materials) under improved grassland in Scotland were analysed. Soil samples represented a wide range of total K concentrations, from 1.3 to 39 g kg − 1 . Quantitative mineralogical data from XRPD were combined with mineral compositions to obtain the mineralogical apportionment of K. Apportionment of K varied significantly, from those soils with almost all K present in various phyllosilicates to others where almost all K is held in K-feldspars. Aqua-regia extractable K is related to K in phyllosilicates (excluding muscovite mica) and unrelated to K in K-feldspars. The studied soils are ranked in terms of their potential capacity to release K based on their mineralogical and geochemical characteristics.

The formulation and use of mixed collectors in sulphide flotation

Mixtures of collectors have been widely used for many years in sulphide flotation, and a range of performance benefits have been reported for many different systems. The combinations of collector types have varied, as have the ratios that have been used. Synergistic effects have been obtained (greater than the sum of the parts) and in some cases the mechanisms of this improved behaviour have been identified. These benefits have been attributed to increased carrying capacity of the froth phase, faster kinetics, and more successful recovery of middling or coarse particles. It is the interaction between the various components of the mixed collector system, rather than the individual main effects, that dominate the performance benefits. The process benefits include increased paymetal recoveries and grades – as well as increased rates of recovery whilst using lower dosages of reagents. Various mechanisms have been reported and are discussed. These have been shown to affect different composition/liberation classes and sizes of mineral particles. In recent years, automated quantitative mineralogy and surface analysis technology such as ToF-SIMS have enabled the development of better information, to establish what aspect of the process has been affected. This has been successful mostly for use in a diagnostic capacity. Candidate selection for the mixed collector suite is presently based on experience and contextual knowledge. Predictive properties from these systems are a desirable future goal. Currently optimum combinations are preferably identified experimentally at laboratory scale prior to any plant trial. It is recommended that such laboratory work be performed using a factorial design with replicates and quality controls, such as may be delivered from High-Confidence Flotation Testing. The purpose of this paper is to summarise and review current theory and practice in the usage of mixtures of collectors in sulphide flotation – both in the application and in research in order to develop insights and guidelines to develop a methodology for use in a predictive capacity. A case study demonstrating this approach will be published at a later date.

Mineralogical characterisation of naturally floatable gangue in Merensky Reef ore flotation

During the recovery of the valuable platinum group minerals and base metal sulphides in the Merensky Reef ore by flotation, a certain amount of naturally floatable gangue (NFG) is recovered, which dilutes the concentrate. Although talc is the only silicate mineral well known for it naturally floatable properties, the proportion of NFG recovered in batch flotation tests of the Merensky ore, however, cannot be solely accounted for by the mass of pure talc present in the feed ore. Using methodology developed at the University of Cape Town to decouple the NFG from entrained gangue recovered in flotation, a series of concentrate samples have been analysed in this study using quantitative mineralogical analysis methods. Results show the major diluents of concentrate grade are orthopyroxene, talc, clinopyroxene and plagioclase in decreasing order of abundance. Orthopyroxene is however, by far the greatest diluent of concentrate grade even though the particles recovered are classified as liberated or high grade middlings. On closer examination, these orthopyroxene particles show a preferential surface association to talc and vice versa which is consistent with the low temperature alteration of anhydrous orthopyroxene to a hydrous phase, namely talc. These composite orthopyroxene particles with partial talc rims are therefore thought to be one of the main contributors to NFG in the Merensky Reef ore.

Importance of Mineralogy in the Geoenvironmental Characterization and Treatment of Chromite Ore Processing Residue

The geoenvironmental characterization of COPR at two deposition sites (New Jersey and Maryland) included geotechnical, chemical, mineralogical, and leaching analyses of three main chromite ore processing residue (COPR) types [gray-black (GB), hard brown (HB), clayey (C)]. Quantitative mineralogical analyses were instrumental in the delineation of the geochemical differences between the three COPR types, which enabled a framework to predict COPR response to potential remediation schemes. Overall, COPR mineralogy resembled cement, with hydration and pozzolanic reactions dominating its geochemistry. GB COPR was largely unreacted despite its prolonged exposure to humid conditions, while HB COPR was completely hydrated and contained high Cr(VI) concentrations. The two materials were chemically similar, with dilution accounting for the chemical and density differences. While the total acid neutralization capacity (ANC) of GB and HB was the same, the ANC at high pH (8–12) was higher in HB due to the dominance of hydrating materials, leading to more buffering capacity and lower Cr(VI) leaching levels. It is concluded that GB and HB were derived from the same ore and process and that postdepositional transformations account for the emergence of HB layers in COPR sites. The physicochemical properties of HB [hardness, high and inaccessible Cr(VI), high ANC] are complicating factors for in situ COPR reductive treatment in the presence of HB.

SEM-based quantitative mineralogical analysis of peridotite, kimberlite, and concentrate

Quantitative automated mineralogy is the acquisition of mineralogical and textural data by scanning electron microscopy-based energy dispersive analytical methods. The technique is used in the metals and energy resource extraction industries to provide accurate mineral characterization information over large data sets. We have employed this method to three projects related to diamonds: mantle peridotite, kimberlite, and garnet concentrate. The first example assesses the metasomatic clinopyroxene-phlogopite modal mineralogy in peridotite xenoliths from Premier/Cullinan (South Africa). Understanding mantle mineral variability can be coupled with measureable mineral properties to develop mantle geophysical and geochemical models. The second example compares kimberlites from Letšeng Satellite Pipe (Lesotho) and Ngamiland (Botswana), to assess the variability of kimberlite mineralogy. Kimberlite domains can be identified on a micro scale with potential to understand parameters such as hardness and grindability, or to identify kimberlite clusters with discrete mineral assemblages. The third example applies mineral compositional variability in garnet concentrate samples as a possible tool for evaluating exploration projects. Application of garnet definitions to concentrates through digitally grouping grains into discrete populations results in improved understanding of large sample populations and hence diamond prospectivity. Quantitative mineralogy applied to diamond-related projects utilizes the principles of geometallurgy in evaluating large data sets for greater understanding of the variability of mantle materials.

Mineralogy of soils from two continental-scale transects across the United States and Canada and its relation to soil geochemistry and climate

Abstract Quantitative mineralogy correlates with major-, minor- and trace-element chemistry for 387 samples of A-horizon and deeper soils collected from east–west and north–south transects across the USA and Canada, where the deeper soils were collected beneath the A-horizon samples. Concentrations of the major elements correlate with specific mineral phases. Minor- and trace-element concentrations correlate with the same phases as the major elements with which they share similar geochemical behavior. Concentrations of quartz and feldspar correlate with precipitation trends east of the Rocky Mountains, and are independent of the underlying rock type and age, indicating that the weathering of soils in this region may have reached a steady-state mineralogy. Other trends in mineralogy relate to physiographic province. The combination of quantitative mineralogy and chemical analysis yields a much richer portrait of soils than can be gained from chemistry alone, because the origins of chemical trends and the chemical availability of specific elements are related to mineralogy.

Application of the Rietveld method for the investigation of mortars: a case study on the archaeological site of Thamusida (Morocco)

This study presents a multi-technique approach to the investigations of mortars, involving the application of the Rietveld method. The quantitative mineralogical analysis of samples was aimed at (1) verifying its significance in relation to results obtained through other techniques and (2) evaluating its potential in mortars characterisation. Six type of mortars used in the Roman settlement of Thamusida (50 km north of Rabat, Morocco) were investigated through X-ray powder-diffraction and Rietveld refinement, optical microscopy, image analysis, scanning electron microscopy, electron microprobe analysis, X-ray fluorescence (XRF) and combined differential thermal, and thermogravimetric analysis (DT–TGA). All the adopted techniques yielded unique results and complementary data; however, the Rietveld method can actually substitute thermal analysis accurately. CaO oxide contents obtained by DT/TGA and Rietveld are in good agreement, but both were only partly comparable to XRF results. In our case, XRF and Rietveld results diverge when binders contain more than 67 wt.% CaO. The discrepancies can mainly be ascribed to the presence of amorphous material and to the obtainable accuracy by QPA-Rietveld method; conversely, the nonstoichiometry of phases does not affect our results, because phases with variable compositions are present in small amounts. Results further showed that the adopted methods were suitable for mortar characterisation. All studied mortars (1) have weak hydraulic properties; (2) employed binders characterised by highly variable CaO contents and by significant amounts of SiO2; (3) used coarse to fine quartz–carbonate-rich sands as the aggregate; and (4) selectively mixed 2 or 3 parts of aggregate with 1 part of binder, depending on the destination of the mortar.

X-ray diffraction and infrared characterization of Oxisols from central and southeastern Brazil

AbstractEleven Oxisols with high clay contents, 2.6–59.7 wt.% Fe2O3, and containing hematite, goethite, magnetite and maghemite, from São Paulo, Minas Gerais and Goiás, Brazil, were studied for the purpose of microwave remote sensing applications in the 0.3 to 300 GHz range. Of special interest are: the pseudosand effect caused by Fe-oxide cementation of clusters of soil particles; the mineralogy; and whether the soil magnetic susceptibility affected by ferromagnetic magnetite and maghemite interferes with microwave propagation. Quantitative mineralogical analyses were conducted using X-ray diffraction with Rietveld refinement. Visible, near infrared and short wave infrared spectroscopic analyses were used to characterize the samples qualitatively for comparison with published spectral radiometry results. Quartz (3–88%), hematite (2–36%) and gibbsite (1–40%) occurred in all soils, whereas kaolinite (2–70%) and anatase (2–13%) occurred in nine samples. Ilmenite (1–8%) was found in eight soils and goethite (2–39%) in seven. Of the ferromagnetic minerals, maghemite occurred in seven soils (1–13%) and three contained magnetite (<2%). These results will be applied to the interpretation of the effect of Fe oxides, particularly the ferromagnetic oxides, on microwave interaction with high-Fe soils, with ultimate application to the monitoring of soil water content by microwave remote sensing.

Toward a Comprehensive Approach to the Collection and Analysis of Pica Substances, with Emphasis on Geophagic Materials

BackgroundPica, the craving and subsequent consumption of non-food substances such as earth, charcoal, and raw starch, has been an enigma for more than 2000 years. Currently, there are little available data for testing major hypotheses about pica because of methodological limitations and lack of attention to the problem.MethodologyIn this paper we critically review procedures and guidelines for interviews and sample collection that are appropriate for a wide variety of pica substances. In addition, we outline methodologies for the physical, mineralogical, and chemical characterization of these substances, with particular focus on geophagic soils and clays. Many of these methods are standard procedures in anthropological, soil, or nutritional sciences, but have rarely or never been applied to the study of pica.Principal FindingsPhysical properties of geophagic materials including color, particle size distribution, consistency and dispersion/flocculation (coagulation) should be assessed by appropriate methods. Quantitative mineralogical analyses by X-ray diffraction should be made on bulk material as well as on separated clay fractions, and the various clay minerals should be characterized by a variety of supplementary tests. Concentrations of minerals should be determined using X-ray fluorescence for non-food substances and inductively coupled plasma–atomic emission spectroscopy for food-like substances. pH, salt content, cation exchange capacity, organic carbon content and labile forms of iron oxide should also be determined. Finally, analyses relating to biological interactions are recommended, including determination of the bioavailability of nutrients and other bioactive components from pica substances, as well as their detoxification capacities and parasitological profiles.SignificanceThis is the first review of appropriate methodologies for the study of human pica. The comprehensive and multi-disciplinary approach to the collection and analysis of pica substances detailed here is a necessary preliminary step to understanding the nutritional enigma of non-food consumption.

Role of Microbial Fe(III) Reduction and Solution Chemistry in Aggregation and Settling of Suspended Particles in the Mississippi River Delta Plain, Louisiana, USA

AbstractRiver-dominated delta areas are primary sites of active biogeochemical cycling, with productivity enhanced by terrestrial inputs of nutrients. Particle aggregation in these areas primarily controls the deposition of suspended particles, yet factors that control particle aggregation and resulting sedimentation in these environments are poorly understood. This study was designed to investigate the role of microbial Fe(III) reduction and solution chemistry in aggregation of suspended particles in the Mississippi Delta. Three representative sites along the salinity gradient were selected and sediments were collected from the sediment-water interface. Based on quantitative mineralogical analyses 88–89 wt.% of all minerals in the sediments are clays, mainly smectite and illite. Consumption of SO42−\$\end{document} and the formation of H2S and pyrite during microbial Fe(III) reduction of the non-sterile sediments by Shewanella putrefaciens CN32 in artificial pore water (APW) media suggest simultaneous sulfate and Fe(III) reduction activity. The pHPZNPC of the sediments was ⩽3.5 and their zeta potentials at the sediment-water interface pH (6.9–7.3) varied from −35 to −45 mV, suggesting that both edges and faces of clay particles have negative surface charge. Therefore, high concentrations of cations in pore water are expected to be a predominant factor in particle aggregation consistent with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Experiments on aggregation of different types of sediments in the same APW composition revealed that the sediment with low zeta potential had a high rate of aggregation. Similarly, addition of external Fe(II) (i.e. not derived from sediments) was normally found to enhance particle aggregation and deposition in all sediments, probably resulting from a decrease in surface potential of particles due to specific Fe(II) sorption. Scanning and transmission electron microscopy (SEM, TEM) images showed predominant face-to-face clay aggregation in native sediments and composite mixtures of biopolymer, bacteria, and clay minerals in the bioreduced sediments. However, a clear need remains for additional information on the conditions, if any, that favor the development of anoxia in deep- and bottom-water bodies supporting Fe(III) reduction and resulting in particle aggregation and sedimentation.

Application of zeolitic volcanic rocks for arsenic removal from water

Natural zeolitic rocks consisting mainly of chabazite-phillipsite, clinoptilolite, and volcanic glass have been evaluated by means of batch methods to remove arsenic from waters with different mineralization degree (from deionized water to natural water with a specific conductivity of 1,600 μS cm − 1 ). Arsenic was previously spiked in the studied waters at concentrations of about 100 µg l − 1 to simulate actual cases. The compositional range of natural waters is representative of large hydrogeochemical regions around the world. The experiments were focussed on the application of natural common zeolitic rocks to water treatment for human consumption. The removal efficiency observed rises, in the better cases, 60–80% for chabazite-phillipsite raw materials whereas is 40–60% for clinoptilolite-bearing ones. The arsenic removal tends to increase with water mineralization degree, independently of the zeolitic rock type. A large zeolitic content in the chabazite-phillipsite raw materials increase the removal. Instead, the inverse situation is observed in the clinoptilolite-bearing rocks. The relevance of the quantitative mineralogical analysis, determining also the content of volcanic glass, as well as the use of natural waters in the removal tests has been demonstrated.

An investigation of the factors affecting the recovery of molybdenite in the Kennecott Utah Copper bulk flotation circuit

The Bingham Canyon mine and associated Copperton Concentrator operations are a significant copper and molybdenum producer. Molybdenum is present in the deposit as the sulphide mineral molybdenite. In 2004, the price of molybdenum increased 10-fold resulting in a renewed emphasis on production of this metal, including efforts to optimize its flotation recovery. Molybdenite recovery in the bulk flotation circuit is consistently lower than that of the copper sulphides as well as being far more variable. This paper describes the systematic use of size recovery data, quantitative mineralogy and surface analysis to identify the factors contributing to molybdenite recovery relative to copper in the Copperton bulk flotation circuit. Several operational changes have been made to capitalize on the findings of the research these include the separate treatment of an ore type containing problematic silicate minerals and the optimization of the frother to collector ratio to ensure adequate froth stability.

Quantitative bulk and single-particle mineralogy of a thick Chinese loess–paleosol section: implications for loess provenance and weathering

A 40 m loess–paleosol section (L1, S1, and upper L2) at the semi-arid western margin of the Chinese Loess Plateau was investigated by quantitative mineralogical, microscopic, and geochemical analyses of bulk samples and single particles. The average ( N=16) mineralogical composition of loess in the studied section is 34.8% quartz, 15.3% plagioclase, 5.0% K-feldspar, 25.1% phyllosilicates, 11.7% calcite, 3.3% dolomite, and 1.9% amphibole. Ratios of plagioclase, K-feldspar, and amphibole to quartz do not change throughout both the loess and paleosol units, while the ratio of total phyllosilicate to quartz is enhanced in the paleosol where there is significant variation in calcite and dolomite contents. Illite and interstratified illite–smectite are the most abundant (84±4%) clay minerals in the clay fraction of both loess and paleosol samples. The calcite/dolomite ratio, Mg/Si ratio, iron oxidation degree, and organic carbon contents are positively correlated to magnetic susceptibility. Weathering and elemental mobilization in paleosol samples was indicated by calcite–dolomite dissolution, nanofiber–calcite reprecipitation, and biotite–hydrobiotite transformation, while there was no notable evidence for weathering observed in loess samples. The essentially pristine state of loess samples with respect to weathering and the minimal alteration of minerals in the paleosol indicate relatively poor weathering conditions at both the depositional and source sites. Analysis of single particles show that most plagioclase is albitic, calcite occurs frequently in particles with dolomite but also with silicates, biotite is associated with barite–celestine inclusions, iron oxide occurs as a pseudomorph after framboidal pyrite, and rock fragments may be siliciclastic sedimentary, metasedimentary, and granitic. These observations indicate that the lithology of source regions must have been dominated by largely siliciclastic and carbonate sedimentary rocks and their low-grade metamorphic equivalents with contributions from granitoids partly affected by hydrothermal alterations and possibly high-grade metamorphic rocks. The mineralogical analysis of loess and paleosols opens new ground for refining the established climatic proxies, and for tracking source lithology and weathering in the source and depositional regions.

Quantitative mineralogical analysis of hydraulic limes by X-ray diffraction

A combined selective dissolution/quantitative X-ray diffraction (QXRD) approach is proposed for the quantitative mineralogical phase analysis of hydraulic limes. The proposed methodology is validated by the analysis of two model mixtures. Afterwards two commercial hydraulic binders and one self-burned hydraulic quicklime were analysed. Chemical, thermal and microprobe analyses were performed to check the results. It is shown that the proposed selective dissolution/QXRD approach yields reliable quantitative mineralogical information for hydraulic limes in spite of their complex phase composition and the presence of amorphous material.

The effect of microwave pretreatment on the liberation of a copper carbonatite ore after milling

The effects of microwave treatment on the liberation spectrum of a rod-milled South African carbonatite ore are presented based on quantitative mineralogical analysis. The treated ore was processed for 0.5 s at 10.5 kW in a single mode microwave cavity in batches of 1 kg. The ore selected for microwave treatment was a sample from a tertiary crusher product stream feed to a rod mill. The treated and untreated ore were subsequently grinded to 80%–800 μm. The microwave treated ore showed a significant increase in the amount of liberated copper minerals in the relatively coarse particle size range (106 to 300 μm). Similar significant shifts in the liberation spectra were noted for all the minerals in the ore. It is inferred that microwave treatment induces changes in the fracture pattern, favouring liberation of microwave susceptible minerals at larger particle sizes.

Relations between elemental content in till, mineralogy of till and bedrock mineralogy in the province of Småland, southern Sweden

Information on soil mineralogy is essential for weathering rate calculations. Quantitative mineralogical analyses are expensive and time-consuming, and thus indirect methods of determining the mineralogical composition are important, for example estimating the composition based on the elemental content in till (total concentrations), or based on information about the underlying bedrock. The mineralogical composition and the elemental content in till were analysed in two areas in southern Sweden, at 10 sites in each area. There were significant differences between the areas regarding both elemental content and optically determined mineralogy. The content of calcium was significantly higher in one area, 5ESV, and there were tendencies in this direction also for magnesium and iron. The potassium content was significantly higher in the other area, 6FNV. The variation in soil chemistry between the areas can be explained by higher contents of the minerals biotite, hornblende and epidote in the first area (5ESV) and higher contents of K-feldspar in the second (6FNV). Normative mineralogy was determined based on the elemental content. A comparison between the normative mineralogy and the optically determined mineralogy showed great similarities which indicates that there is good potential for using elemental content for estimating the mineralogical composition. The difference in till composition between the areas could not be explained by the underlying bedrock, which indicates that the information available on the bedrock is not sufficient for estimation of the till mineralogical composition.

Comparative quantitative petrographical analysis of Cenozoic aquifer sands in Flanders (N Belgium): overall trends and quality assessment

The bulk mineralogy and grain size distribution of 30 sands of the Belgian Cenozoic were studied. From each sample, the grain size distribution was defined both by classical sieving and image analysis (IA) of thin sections. The grain size distribution by means of automated IA produces an overestimation of the smaller grain sizes; this is related to the artificial breaking up of heterogeneous grains and to the random sectioning of the grains in thin section. However, the results of the quantitative mineralogical analysis of the sands obtained through point counting indicate overall depositional or diagenetical influences. Continentally influenced sands are characterized by a high quartz content, whereas marine-influenced sands reveal a more diverse mineralogy. The potentially reactive chert content generally lies under 2%. Sedimentological and diagenetical influences on the mineralogy and physical properties of the sands thus control the applicability of such materials as building sands.

Weathering of Fe-bearing minerals under Martian conditions, investigated by Mössbauer spectroscopy

The surface of Mars is covered by weathered material. Mars' rusty red colour in particular is commonly ascribed to ferric iron-bearing minerals. The planet's surface is generally iron rich. Mössbauer spectroscopy is a powerful tool for quantitative mineralogical analysis of Fe-bearing minerals. Consequently, the miniaturized Mössbauer spectrometer MIMOS II is part of the payload of NASA's twin Mars Exploration Rovers “Spirit” and “Opportunity”, and ESA's ill-fated Mars Express lander “Beagle 2”. Both Mars Exploration Rovers are currently conducting successful surface operations on Mars. In this paper, we give a brief insight into mission operations with respect to the reconstruction of local weathering scenarios at the landing sites, which in turn will help to illuminate the climatic history of the planet. Mössbauer spectra obtained in preparation of the mission from the SNC meteorites Nakhla, Dar al Gani 476, and Sayh al Uhaymir, show weathering and other alteration features. Preliminary results of laboratory weathering experiments on Fe-bearing minerals (olivine and pyroxene) show the importance of analysing individual minerals to understand weathering of more complex mineral assemblages like, e.g., basalt.

Quantitative mineralogical analysis of Spanish roofing slates using the Rietveld method and X-ray powder diffraction data

The relative proportions of the minerals in a series of slates from the Iberian Massif in northwestern Spain, quarried and used for roofing purposes, have been evaluated using X-ray powder diffraction and the Rietveld-based SIROQUANT data processing system. Information on the chemical composition of the chlorite, mica and feldspar in the slates was obtained separately from electron microprobe studies, and was used in conjunction with the mineral proportions to calculate an inferred chemical composition for each sample from the quantitative XRD data. The inferred compositions were then compared to the actual chemical compositions of the respective slate samples, obtained by X-ray fluorescence spectrometry, to evaluate the consistency between the XRD results and independent chemical analysis data. A high level of consistency was observed between the element oxide percentages inferred from the XRD study and the equivalent oxide proportions determined by direct chemical analysis. The comparison suggests that Rietveld-based interpretation of X-ray powder diffraction data provides results that are consistent with other compositional parameters. Although no particular relationships were observed among the individual mineral percentages in the slates of the sample suite, a well-defined inverse relationship was found between the percentages of quartz plus feldspar on the one hand and the percentages of mica plus chlorite on the other. This may reflect variations in the relative proportions of coarse- and fine-grained sediment in the original parent materials that formed the slate deposits. Resumen Se han calculado las proporciones relativas de los diferentes minerales de las pizarras de techar explotadas en el Macizo Iberico del noroeste de Espana. Para ello, datos obtenidos por difraccion de rayos X sobre muestras de polvo de pizarra han sido procesados utilizando el sistema SIROQUANT, basado en la tecnica de Rietveld. A partir de estudios de microsonda electronica se determino la composicion quĺmica de cloritas, micas y feldespatos de las pizarras, lo que junto con las proporciones minerales obtenidas a partir de los datos de DRX, permitio inferir una composicion quĺmica para cada muestra de pizarra. Estas composiciones inferidas fueron entonces comparadas con composiciones quĺmicas de las respectivas muestras de pizarra, obtenidas mediante fluorescencia de rayos X, evaluandose la coherencia entre los resultados de las dos tecnicas empleadas. Un alto nivel de coherencia fue observado entre los porcentajes de oxidos de cada elemento inferidos a partir del estudio de DRX y las proporciones de oxido equivalentes determinadas por FRX. La comparacion sugiere que la interpretacion de la DRX basada en la tecnica de Rietveld aporta resultados que son coherentes con otros parametros composicionales. Aunque no se observaron relaciones entre porcentajes de minerales individuales en las pizarras muestreadas, se encontro una relacion inversa bien definida entre los porcentajes de cuarzo mas feldespato y los porcentajes de mica mas clorita, lo que se interpreta como una herencia de las proporciones relativas de limo y arcilla en los sedimentos a partir de los que se formaron las pizarras.