Person:
García Rivas, Javier

First Name

Javier

Last Name

García Rivas

URI

https://hdl.handle.net/20.500.14352/80978

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Geológicas

Department

Mineralogía y Petrología

Area

Cristalografía y Mineralogía

Identifiers

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Now showing 1 - 10 of 15

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.
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, Eduardo
41 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.
Crystal–chemical and diffraction analyses of Maya blue suggesting a different provenance of the palygorskite found in Aztec pigments
(Archaeometry, 2021) Sánchez del Río, Manuel; García Rivas, Javier; Súarez Barrios, Mercedes; García Romero, Emilia
Maya blue is a pigment found in different archaeological sites of different cultures from Mesoamerica, and also in colonial buildings in Mexico and Cuba. The pigment is made from a thermally treated mixture of indigo and palygorskite. Pigment samples from Aztec and non‐Aztec archaeological sites as well as reference Yucatecan palygorskites were studied in this paper to assess their differences. The characterization of the samples was carried out by a combination of a crystal–chemical‐point analyses using electron microscopy to obtain the structural formulae of the palygorskite crystals, and studied using high‐resolution X‐ray diffraction. The data show evidence that the palygorskite used by non‐Aztec cultures, such as the Maya, is compatible with palygorskite from known sources in the Yucatan Peninsula, while the palygorskite used by the Aztec culture is different in its structure and has an origin that is still unknown.
Review and new data on the surface properties of palygorskite: A comparative study
(Applied clay science, 2021) Súarez Barrios, Mercedes; García Rivas, Javier; Morales, Juan; Lorenzo, Adrián; García Vicente, Andrea; García Romero, Emilia
Palygorskite is a mineral used in a wide number of industrial sectors. Currently, there are hundreds of studies in which palygorskite is a part of different nanocomposites and bionanocomposites. The surface properties are essential for these applications, and in this work, an in-depth revision of these properties is done, showing that the high variability found cannot be explained only by the number of impurities or by differences in the analysis conditions. To further deepen the knowledge of the surface properties of palygorskite and palygorskitic clays, a comparative study of a wide group of high purity samples is also performed, and new data on these surface properties are provided with the determination of the specific surface area (SSA), micropore surface area (SSAμp), micropore volume (Vμp), external surface area (SSAEx), and mean equivalent pore diameter. Both the bibliographic data and new data show that SSA varies from a few tens of m2g−1 to almost 300 m2g−1, and the microporosity and external surface proportions also vary greatly. The experimental data obtained show that 1) ordinary soft vacuum conditions produce structural folding, which limits the accessibility to the inner part of the structural tunnels; 2) microporosity is related to the intra- and inter-fibre microporosity, depending first on the fibre size, because the shorter the fibre, the higher the partial accessibility to the entrance of the channels; 3) the crystal chemistry of the samples also influences the SSA because the Mg-rich terms, which have higher content of sepiolite polysome proportions in their structure as well as wider and more accessible intracrystalline channels than palygorskite polysomes.
New data on the microporosity of bentonites
(Engineering geology, 2022) Súarez Barrios, Mercedes; Lorenzo, Adrián; García Vicente, Andrea; Morales, Juan; García Rivas, Javier; García Romero, Emilia
This comparative study on a very wide group of samples shows that the crystal size and crystalline defects of smectites influence microporosity of bentonite considerably more than previously considered. The smectite crystals and surface properties, including microporosity and micropore volume, were studied using high resolution transmission electron microscopy and N2 adsorption, respectively. The specific surface area obtained varied between 25 and 278 m2g−1. The micropore area ranged between 6 and 76 m2g−1, and the external area ranged from 18 to 208 m2g−1. The external surface area was related to the size of the crystals in [001] direction because of the smaller particles with few stacked 2:1 layers have more basal surfaces accessible to the N2 molecules. However, the microporosity can be related to 1) the size of the crystals, owing to the partial ability of N2 to penetrate into the interlayer space, 2) the abundance of crystalline defects affecting the stacking of the 2:1 layers, and 3) the arrangement of the crystals forming particles, in which sub-parallel aggregates generate micro and mesopores. The study shows that these bentonites have pores in the full range, from smaller micropores (related to the crystalline structure in the interior of the interlayer) to micrometric macropores. The amounts of micro, meso, and macropores varied between samples but were similar and characteristic for samples from the same geological area.
Project number: 231
Creación de una Colección Multimedia de Minerales al Microscopio Petrográfico: Un Aspecto Central en la Formación en Geociencias
(2023) Pérez Garrido, Carlos; García Rivas, Javier; Forjanes Pérez, Pablo Cayetano; Luque Del Villar, Francisco Javier; Fernández Díaz, María Lourdes; Astilleros García-Monge, José Manuel; Yesares Ortiz, María Dolores; Carmona Tijerín, Victor; Esteban Ruiz, Paula; Fernández Riveras, Camila Isabel; García Herrador, Miguel; Sánchez Acosta, Rubén; Garrido Sánchez, Azael
Este Proyecto Innova Docente tiene como objetivo realizar una labor apenas desarrollada hasta ahora: la digitalización de muestras de minerales transparentes de la colección de las asignaturas “Mineralogía I” de GG y “Cristalografía y Mineralogía” de GIG del Departamento de Mineralogía y Petrología de la UCM. A través de la digitalización de las muestras (fotos y vídeos) se busca crear un repositorio (accesible a través de la página web del departamento y material para el Campus Virtual de las asignaturas implicadas) en el que los estudiantes puedan consultar fácilmente las propiedades ópticas de los minerales vistos en prácticas, incluyendo sus cambios en función de las diferentes orientaciones. Este repositorio multimedia pretende marcar una clara diferencia con otros repositorios de otras universidades, en los cuáles únicamente se dispone de fotografías, las cuales por si solas no permiten observar claramente muchas de las características distintivas en minerales anisótropos. Consideramos que la digitalización de estas colecciones serán de gran ayuda para el adecuado aprendizaje y estudio de las diferentes asignaturas que utilizan la microscopía de luz transmitida, ya que la accesibilidad a este tipo de microscopios por parte de los alumnos fuera de la universidad es nula o muy limitada. Además, estos materiales serán esenciales en caso de suspensión de la actividad presencial o como apoyo a las actividades realizadas por los alumnos en el aula. También se pretende involucrar a estudiantes de las asignaturas en cuestión en el desarrollo de este Proyecto, tanto los incluidos en la convocatoria como otros alumnos de la asignatura que, a posteriori, quieran sumarse a la tarea.
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, Mercedes
In 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.
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, Emilia
On the structural formula of smectites: a review and new data on the influence of exchangeable cations
(Journal of Applied Crystallography, 2021) García Romero, Emilia; Lorenzo, Adrián; García Vicente, Andrea; Morales, Juan; García Rivas, Javier; Súarez Barrios, Mercedes
The understanding of the structural formula of smectite minerals is basic to predicting their physicochemical properties, which depend on the location of the cation substitutions within their 2:1 layer. This implies knowing the correct distribution and structural positions of the cations, which allows assigning the source of the layer charge of the tetrahedral or octahedral sheet, determining the total number of octahedral cations and, consequently, knowing the type of smectite. However, sometimes the structural formula obtained is not accurate. A key reason for the complexity of obtaining the correct structural formula is the presence of different exchangeable cations, especially Mg. Most smectites, to some extent, contain Mg2+ that can be on both octahedral and interlayer positions. This indeterminacy can lead to errors when constructing the structural formula. To estimate the correct position of the Mg2+ ions, that is their distribution over the octahedral and interlayer positions, it is necessary to substitute the interlayer Mg2+ and work with samples saturated with a known cation (homoionic samples). Seven smectites of the dioctahedral and trioctahedral types were homoionized with Ca2+, substituting the natural exchangeable cations. Several differences were found between the formulae obtained for the natural and Ca2+ homoionic samples. Both layer and interlayer charges increased, and the calculated numbers of octahedral cations in the homoionic samples were closer to four and six in the dioctahedral and trioctahedral smectites, respectively, with respect to the values calculated in the non-homoionic samples. This change was not limited to the octahedral sheet and interlayer, because the tetrahedral content also changed. For both dioctahedral and trioctahedral samples, the structural formulae improved considerably after homoionization of the samples, although higher accuracy was obtained the more magnesic and trioctahedral the smectites were. Additionally, the changes in the structural formulae sometimes resulted in changing the classification of the smectite.
VNIR-SWIR spectroscopic study of samples from the sepiolite-palygorskite polysomatic series
(Macla, 2022) García Rivas, Javier; García Romero, Emilia; Santamaría López, Ángel; Súarez Barrios, Mercedes