Person: García Rivas, Javier
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First Name
Javier
Last Name
García Rivas
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Geológicas
Department
Mineralogía y Petrología
Area
Cristalografía y Mineralogía
Identifiers
7 results
Search Results
Now showing 1 - 7 of 7
Item Crystalochemical Complexity of Magnesic Clays from the Tajo Basin(Macla: revista de la Sociedad Española de Mineralogía, 2014) García Rivas, Javier; Súarez Barrios, Mercedes; García Romero, EmiliaItem An insight in the structure of a palygorskite from Palygorskaja: Some questions on the standard model(Applied clay science, 2017) García Rivas, Javier; Sánchez del Río, Manuel; García Romero, Emilia; Suárez, MercedesIn this study we analyze in detail a palygorskite from Palygorskaja. This palygorskite is situated in the context of the existing studies using X-ray powder diffraction analysis. Moreover, a novel microdiffraction study on a small bunch of fibers shows highly structured 2D diffraction patterns that allow to decipher some information on the microstructure, thus overcoming the uncertainty usually originated by large samples containing mixtures and impurities. Structural data provided by Chisholm (1992) are used to simulate 1D and 2D powder and fiber diffraction patterns for palygorskite, which are compared with the experimental results. We performed simulations for powder and fiber diffraction and we centered our attention in the region of interest with d-spacings between 4.0 and 4.5 Å. This palygorskite is consistent with a purely orthorhombic palygorskite, based on good agreement of data with simulations. The experimental results present some reflections not found in the simulations. These reflections are interpreted as corresponding to other hk1 planes of palygorskite. They do not match any reflection from the monoclinic structural model nor from probable impurities, reinforcing the interpretation of them being intrinsic to the structure of the mineral. Our findings suggest a revisal of the commonly accepted structure of palygorskite. They correspond to hk1 planes of palygorskite, and they do not match any reflection neither from the monoclinic structural model nor from possible impurities, and thus reinforcing the idea of them being intrinsic to the structure of the mineral, suggesting the necessity of a revisal of the commonly accepted structure of palygorskite.Item Mineralogical characterisation and surface properties of sepiolite from Polatli (Turkey)(Applied clay science, 2016) Súarez Barrios, Mercedes; García Rivas, Javier; García Romero, Emilia; Jara, N.Sepiolite is one of the most important industrial minerals, due primarily to its surface properties related to its structure. Sepiolite contains alternating 2:1 polysomes that produce tunnels at the inner part of the fibre and channels at the edge of the fibre. Sepiolite is a mineral with notably wide variations in the crystal-chemistry, crystallinity and texture, depending on the formation conditions, which results in highly different characteristics and properties. In this work, six sepiolite samples from the Polatli area (Turkey) are studied, comparing their mineralogical and textural features. The mineralogical composition of the samples is similar: carbonates constitute the main impurities, dolomite appears in all samples studied in different proportions, and small amounts of calcite, quartz and palygorskite have been identified. There is a variation in almost all the reflections of sepiolite, the 110 d-spacing ranges between 12.31 Å and 12.05 Å, this variation is related to the crystal-chemistry of the mineral. The impurities are clearly identified in the IR spectra, in which in addition to the carbonates the presence of the palygorskite polysomes is also detected by the band located at ~ 3620 cm− 1. The differences in the surface properties found in this study (specific surface area between 122 m2 g− 1 and 376 m2 g− 1 and microporous area between 55 m2 g− 1 and 168 m2 g− 1) cannot be related only with the content in impurities, but with the texture and the possible presence of intergrowths.Item Identification and classification of mineralogical associations by VNIR-SWIR spectroscopy in the Tajo basin (Spain)(International journal of applied earth observation and geoinformation, 2018) García Rivas, Javier; Suárez, Mercedes; García Romero, Emilia; García Meléndez, Eduardo41 soil samples were collected at the Tajo Basin (Spain), in an area where Mg-rich clays are benefitted, whit the aim of studying their spectral response in the Visible, Near Infrared (VNIR) – Short Wave Infrared (SWIR) range (350–2500 nm) in terms of mineralogical composition and exploring the possibility of using these data as the basis of a geological mapping through hyperspectral imaging in this wavenumber interval in future research. The samples, belonging to nine different stratigraphic units, were characterized by X-Ray diffraction and VNIR – SWIR laboratory reflectance spectroscopy. The mineralogical associations are formed by complex mixtures of carbonates, gypsum, quartz, feldspars, illite, and smectites in variable proportions depending on the stratigraphic unit. The samples were classified into different groups and subgroups according to their spectral response. The resulting groups allow to extrapolate certain type-spectra to different mineralogical associations corresponding to the stratigraphic units sampled within the area of study. This work is of upmost importance for future works through remote-sensing techniques using VNIR – SWIR imaging of the area. The classification of the samples in different groups, according to their spectral response, and their attribution to the different stratigraphic units sampled, according to their mineralogical content, could help improve the geological mapping of the area of study as well as detecting deposits of Mg-rich clays of economic interest.Item Spanish Bentonites: A Review and New Data on Their Geology, Mineralogy, and Crystal Chemistry(Minerals, 2019) García Romero, Emilia; Manchado, Eva María; Suárez, Mercedes; García Rivas, JavierA review and a synthesis of the geological, mineralogical, and crystal chemical data available in the literature on active Spanish bentonitic exploitations were done, and at the same time, new data are provided from a set of representative samples from these deposits. They were located in three different areas with different geological origins: (1) Miocene sedimentary deposits from the Tajo Basin (Madrid–Toledo provinces) in the center of the Iberian Peninsula, where bentonites appear in two different units named for their colors (Green Clays and Pink Clays); (2) samples from Tamame de Sayago (Zamora province) originating from the hydrothermal alteration of granitic Variscan rocks; and 3) Miocene deposits originating from the hydrothermal alteration of volcanic or subvolcanic rocks from the Cabo de Gata volcanic area (Almería Province) in the southern part of Spain, where the three main deposits (Cortijo de Archidona, Los Trancos, and Morrón de Mateo) were studied. The bentonites from the Tajo Basin were formed mainly by trioctahedral smectites, and there were significant mineralogical differences between the Green and Pink Clays, both in terms of the contents of impurities and in terms of smectite crystallochemistry and crystallinity. The smectites from Tamame de Sayago were dioctahedral (montmorillonite–beidellite series), and they appeared with kaolinite, quartz, and mica in all possible proportions, from almost pure bentonite to kaolin. Finally, the compositions of the bentonites from the three studied deposits in Cabo de Gata were quite similar, and zeolites and plagioclases were the main impurities. The structural formulae of the smectites from Cortijo de Archidona and Los Trancos showed a continuous compositional variation in beidellite–montmorillonite, while in Morrón de Mateo, the smectites were mainly montmorillonite, although there was continuous compositional variation from Al montmorillonites to Fe–Mg-rich saponites. The variation in the smectite composition is due to the intrusion of a volcanic dome, which brings new fluids that alter the initial composition of the smectites.Item Caracterización de palygorskitas españolas(Macla: revista de la Sociedad Española de Mineralogía, 2014) García Romero, Emilia; García Rivas, Javier; Síarez Barrios, MercedesItem Spanish palygorskites: geological setting, mineralogical, textural and crystal-chemical characterization(European Journal of Mineralogy, 2018) Suárez, Mercedes; García Rivas, Javier; Sánchez Migallón, Juan Morales; García Romero, EmiliaA representative group of palygorskites from the six most important Spanish deposits and six other occurrences were studied comparing their mineralogy, textural features, crystal-chemistry, and surface properties. These palygorskites have different geological origin: (1) sedimentary in large Tertiary continental basins, (2) hydrothermally altered volcanic rocks in the southern Spanish Peninsula, also Tertiary in age; and (3) fault-hosted pure palygorskites. The most common impurities are quartz and carbonates, both calcite and dolomite, but also feldspar, illite, smectite, and sepiolite have been identified. The structural formulae obtained show great variability between samples, as well as with respect to the theoretical formula for palygorskite, as they range from magnesian to aluminous palygorskites. The most common fibre length ranges between 1 and 10 µm but the palygorskites of hydrothermal origin are much longer, with lengths over 10 µm. The shorter fibres give rise to tightened textures, while longer fibres usually generate more open textures. These properties, along with the degree of compaction, condition the porosity of the sample, which in turn influences its surface properties. The specific surface areas obtained range between 30 m2 g−1 and 263 m2 g−1, depending on the impurities content and on the texture and crystal-chemistry; the highest values correspond to Mg-rich palygorskite.