Mineral and textural transformations in aluminium-rich clays during ceramic firing

The aim of this study has been to analyse the mineralogical and textural transformations of a set of aluminium-rich shales of interest for refractory and ceramic uses, fired from 800 °C to 1300 °C. To that end, raw and fired samples were analysed by X-ray diffraction, transmitted light microscopy, field emission scanning electron microscopy, and transmission electron microscopy. Raw samples comprise variable proportions of illite, pyrophyllite, orthoclase, quartz, kaolinite, mixed-layer I-Sm, and organic matter. At temperatures below 800 °C, kaolinite, mixed-layer I-Sm, and organic matter are destabilized, indicating that they are the least stable phases in the firing process. Illite, pyrophyllite, and orthoclase remain until 1000 °C and show a broader stability field during firing than in natural environments. Quartz persists throughout the entire firing process, although it is partly replaced by vitreous phase. Hematite crystallizes at 900 °C. Vitrification begins at 1000 °C, marking the first significant textural change. From 1000 °C mullite starts to crystallize from the Si- and Al-rich vitreous phase. The mullite composition is not stoichiometric and probably as temperature increases Si is partially replaced by Al, Fe and Ti in the structure. Nevertheless, with the increase of the firing temperature, the mullite composition is closer to the theoretical composition and also to that of natural mullites. Furthermore its crystal thickness increases with temperature up to 70 nm

Arcillas industriales: mineralogía, propiedades físicas y químicas y usos

Estudio de siete diferentes muestras de arcillas industriales suministradas por varias empresas españolas, con el fin de analizar su mineralogía, sus propiedades físicas y químicas y sus posibles usos. Los análisis de las muestras se han llevado a cabo utilizando las técnicas de laboratorio de difracción de rayos-X, microscopio electroníca de barrido de emisión de campo, capacidad de intercambio de cationes y cationes intercambiables y finalmente adsorción-deserción de N

Transformaciones minerales durante los procesos de cocción de arcillas alumínicas y su relación con propiedades físicas de interés

Mineralogical and textural transformations and changes in physical properties of three shales fired from 800 to 1300ºC have been studied. Initially these samples were formed by variable proportions of illite, pyrophyllite, orthoclase, quartz, kaolinite, mixed layers I/S and organic matter. Raw and fired samples were analysed by X-ray diffraction, transmitted light microscopy, field emission scanning electron microscopy and transmission electron microscopy. Kaolinite, mixed layers I/S and organic matter were destabilized at temperatures below 800°C indicating that they are the least stable phases to the firing process. Illite, pyrophyllite and orthoclase remain until 1000ºC and they show a larger stability field during the ceramic process than in natural environments. Quartz remains during all the firing process, although it is partly replaced by vitreous material. When temperature increases, hematite and mullite crystallize and the vitrification starts from 1000ºC. This vitreous phase is the precursor of mullite. Changes in colour (grey-orange-brown) are due to the loss of organic matter, to the formation of hematite and its subsequent destabilization. Variations in linear contraction, density, total porosity and in average pore size are related to the destabilization of the different phases, the progress of vitrification and the crystallization of mullite

Textura y Composición Mineral de Pizarras de Techar: Estudio con Microscopía Óptica, SEM, EMPA y TEM

[ES] Las pizarras comerciales son rocas de grano muy fino, con una esquistosidad del tipo slaty cleavage y una alta fisibilidad, condicionada por la microtextura de la roca (Barros et al., 1985). España es primer productor mundial de pizarras para cubiertas, con 114 plantas y más de 6.100 empleados. La producción anual de pizarra se ha venido incrementando hasta alcanzar en 2007 las 943 Kt (Federación Española de la Piedra Natural, 2008), con una facturación en torno a 400 M€/año. Gran parte de los yacimientos españoles de pizarra se concentran en la Zona Centroibérica (ZCI) del Macizo Ibérico, especialmente en el Dominio del Sinclinal de Truchas. Numerosas canteras se ubican también en la Zona Asturoccidental-leonesa (ZAOL). La mayor parte de las pizarras explotadas en el NO de España y todas las muestreadas en este trabajo son de edad ordovícica (Tabla 1), procediendo estas de las Formaciones Luarca, Casaio, Rozadais y Losadilla (Marcos, 1973; Barros, 1989).SIEl presente trabajo se ha financiado mediante el proyecto CGL2007- 60035/BTE del Ministerio de Ciencia e Innovación

XRD, electron microscopy (EMPA, SEM, TEM) and XRF characterization of roofing slates from NW Spain

[EN] The aim of this paper is to characterize thoroughly the mineralogy and petrography of a set of ten different types of commercial roofing slates from the NW of Spain. Representative samples of each type have been studied by transmitted and reflected-light optical microscopy, scanning and transmission electron microscopy, electron microprobe, X-ray fluorescence and X-ray diffraction techniques. Quantitative analyses of the main mineral percentages in each slate sample were made from XRD data using the Siroquant™ interpretation software system, based on Rietveld principles. The microscopic textures of the slates vary depending on the samples, and lepidoblastic to porphyroblastic textures have been described. Some slates with bands of sand layers display grano-lepidoblastic textures. White mica, quartz, chlorite and feldspar (albite) are the main minerals. The white micas and the chlorites have similar compositions in all the analyzed samples. Electron microprobe analyses indicate that the micas are K-rich dioctahedral varieties, having a composition close to muscovite with a phengitic component. They show the following average formula: (Na0.16 K1.39 Ca0.01) (Al3.83 Ti0.03 Fe0.15 Mg0.14) (Si6.22 Al1.78) O20 (OH)4. The chlorites are magnesian chamosites with an average formula of (Na0.02 K0.04 Ca0.01Al3.24 Ti0.01 Fe5.13 Mn0.03 Mg3.28) (Si5.23 Al2.77) O20 (OH)16. Accessory minerals are ilmenite, rutile, sulphides, carbonates, graphite, monazite, apatite, zircon and tourmaline. Two different associations of sulphide minerals are distinguished: 1) Type I with pyrite, pyrrhotite, pentlandite, cobaltite, chalcopyrite, sphalerite, galena, ullmannite and gersdorffite occurring as pre-kinematic porphydic aggregates; b) Type II mainly with post-kinematic pyrite and sporadic chalcopyrite and galena. The main carbonate mineral is ankerite ((Mg0.26, Ca0.49, Mn0.05, Fe0.19) CO3) with minor calcite and siderite also present.S

Genesis and stability of textural pedofeatures along a soil transect in the siliceous Iberian Chain (NE Spain)

Textural features are widespread in many soils, provide pedogenetic evidence, and are fundamental in soil classification systems. The presence of these features and their conservation over time require certain processes and soil forming factors. This study investigates the genesis of textural pedofeatures, especially clay coatings, and the stressful conditions that can eventually lead to their disappearance. To achieve this goal, four profiles with clay-enriched horizons have been studied (macro- and micromorphology, physical, chemical and mineralogical properties and classification) along a transect in the siliceous Iberian Chain (NE-Spain). The profiles, which have unmistakable illuvial accumulations in various horizons (Bhs, Bt, Btk), are classified (ST/WRB) as: a Spodosol/Podzol in the headslope, two Alfisol/Luvisols in the backslope and an Alfisol/Calcisol in the footslope. For the latter soil, the apparently strong difference in their classification to the first hierarchical level is due to the weight that the WRB places on the presence of an argic recarbonated horizon on a calcic horizon. Clay illuviation was identified in all the soils, with coatings and infillings of microlaminated clay. These clayey pedofeatures are mostly mechanically fragmented or deformed, which is micromorphologically evidenced by an undulating, wavy extinction that does not run completely parallel to the surfaces they cover. Different destructive processes are identified along the soil transect; so, cryoturbation is the dominant process in the Podzol located at the highest elevation (Moncayo Massif). Instead, the clay coatings in the Btk horizon of the footslope (Calcisol) are covered and deformed by the growth of secondary calcite. The textural pedofeatures in this soil, which is very clayey, can also undergo argilloturbation processes, like in the backslope soils (Luvisols). In conclusion, several ongoing stress processes, that sometimes require different environmental conditions (polygenetic), affect most textural pedofeatures and lead to their progressive alteration and disappearance.Different projects of the Research Results Transfer Office of the University of Zaragoza (Ref. 2017/0535, ref. 2018/0416; ref. UZ2020-TEC-01) provided financial support for this research

Alteración hidrotermal en yacimientos epitermales desarrollada en rocas básicas.

Identificación y caracterización los procesos de alteración hidrotermal de las rocas encajantes de la veta Josefa (andesitas), perteneciente a Mina Martha, Macizo del Deseado (Patagonia Argentina)

Paleohistología y permineralización de dos saurópodos del ciclo Jurásico en la subcuenca de Galve (Teruel, España)

En este trabajo se realiza una aproximación a la paleohistología de dos dinosaurios saurópodos, Galvesaurus herreroi Barco et al., 2005 y un saurópodo indeterminado. El primero procede del yacimiento Cuesta Lonsal de Galve (Teruel) de edad Kimmeridgiense superior mientras que el segundo se ha encontrado en el yacimiento La Peñuela en Camarillas (Teruel) cuya de edad es Berriasiense. Las observaciones histológicas realizadas a partir de láminas delgadas de los restos óseos en microscopio óptico, han permitido determinar el estadio ontogenético de los saurópodos en el momento de su muerte, tratándose en Galvesaurus y el saurópodo de La Peñuela de ejemplares adulto y senil, respectivamente. Así mismo, se ha realizado un estudio mineralógico de las muestras paleohistológicas combinando la microscopía óptica y electrónica de barrido de emisión de campo (FESEM). En el estudio se observa que los procesos diagenéticos son similares en los restos óseos de los dos ejemplares. El apatito que compone los huesos no ha sido modificado durante la diagénesis. Los rellenos en los canales y cavidades vasculares son mayoritariamente cementos calcíticos, granos detríticos y óxidos. El hecho de que los procesos observados sean similares en los distintos individuos se debe probablemente a la similitud litológica y de historia geológica de las formaciones en las que los ejemplares fueron encontrados.In this work a paleohistological approach to two sauropod dinosaurs, Galvesaurus herreroi Barco et al., 2005 and an undescribed specimen have been performed. The former comes from the Cuesta Lonsal site in Galve (Teruel) and it is late Kimmeridgian in age whereas the latter have been found in La Peñuela site in Camarillas (Teruel) and it is Berriasian in age. The histological observations of the skeletal remains that were made from the thin sections in an optical microscope have allowed to determine the ontogenetic stage of the sauropods at the time of their death: Galvesaurus and the sauropod of La Peñuela were adult and senile specimens, respectively. A mineralogical study of the paleohistological samples has also been carried out, combining optical and field emission scanning microscopy (FESEM). In the study it is observed that the diagenetic processes are similar in the bone remains of the two specimens. The apatite of the bones has not been modified during diagenesis. The fillings in vascular channels and cavities are mainly calcite cements, detrital grains and oxides. The fact that the observed processes are similar in the two individuals is probably due to the lithological similarity and the geological history of the formations in which the specimens were collected

Evolution of Clays in Cretaceous Marly Series (Álava Block, Basque Cantabrian Basin, Spain): Diagenesis and Detrital Input Control

Two stratigraphic sections of carbonate sediments with significant thickness differences and without appreciable tectonic deformation were studied near the trough and on a threshold zone at the Álava Trough. Such characteristics make them appropriate to analyze the influence of a slow progression of the diagenesis over the original clay suite. X Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Analytical Electron Microscopy (AEM) techniques were applied in natural and alkylammonium-treated samples. Diagenesis slightly modified the clay mineralogy, the disappearance of smectite, and the variation in the content and ordering of the I/S mixed layer, with burial being the most noteworthy process. The total charge in the 2:1 expandable layers of smectite and I/S shows a slight increase, preferentially located on tetrahedral sheets, with depth. The data suggest a moderate diagenesis grade for the studied materials. The combination of techniques allowed identification of several types of detrital micaceous phases, as well-crystallized K-rich micas, Na-K micas, mica-chlorite stacks, and illites, with an expandable behaviour after the alkylammonium treatment. The total charge of illites did not change with diagenesis, suggesting their detrital origin. This research shows that the detrital assemblage masks the diagenetic evolution in the basin, which indicates the importance of the combination of different techniques to infer correctly the diagenetic grade in a sedimentary basin.This research was funded by the Spanish Government FEDER project CGL 2015-65404-R/BTE, CGL2016-75679-P, by the Basque Government project IT930-16, Research Group RNM-179 of the Junta de Andalucía and the Aragon Government project E18_17R

Alteración hidrotermal en yacimientos epitermales desarrollada en rocas ácidas (Macizo del Deseado, Argentina)

The main objectives of the present project are the identification and description of the mineralogy and textural changes generated by hydrothermal alteration on several volcanosedimentary rock samples from the Chon Aike and La Matilde Jurassic formations located at the “El Deseado” mining district (Argentina). In order to get the aforementioned objectives, a series of analytical steps have been taken, which include transmitted-light and reflected-light microscopical studies, x-ray diffraction analyses and the use of a field emission scanning electron microscope. The studied samples are crystalline lapilli tuffs and coarse and fine grained crystalline tuffs. The igneous phases found include potassium feldspar, muscovite and quartz phenocrysts, glass fragments and rock fragments. The matrix of these samples is sometimes it is isotropic, which indicates the presence of glass. These rocks have undergone hydrothermal alteration processes which can be observed mainly on the potassium feldspars, muscovites, glass fragments and the matrix. These phases have been replaced by illite, kaolinite and illite-smectite mixed layers, as well as goethite, Fe-Ti oxides, rutile, quartz and alunite group minerals. The studied samples, taken from 2 different areas of Martha Vein system, show that the distribution of the hydrothermal mineralogy differs depending on its proximity to the vein. Close to the vein, the potassium feldspar phenocrysts have been partially replaced by several clay minerals, including kaolinite, which evidences an argillic alteration type. Far away from the vein, the phenocrysts exhibit a greater degree of alteration, and are characterized by an association of illite, kaolinite and alunite group minerals (alunite-crandallite). This indicates a change towards an advanced argillic alteration type. In the eastern part of Martha Vein (Samples ME-19, ME-28 and ME-49), a silicic alteration type can be observed towards the distal area of the Vein. This alteration results in vuggy quartz and silica sinter (massive quartz). The textural and mineralogical differences found in the studied samples reflect the physico-chemical properties of the fluid which gave rise to the alterations. In the northern area of Martha Vein, the presence of kaolinite and alunite indicates an acid pH (3-5) and temperatures lower than 250ºc. On the other hand, the presence of silica sinters and vuggy quartz in the eastern area of the vein indicates that the pH of the fluids evolved towards lower values (pH<3). The features exhibited by the studied alterations correspond to high sulphidation epithermal deposits