Macroscopic palygorskite from Lisbom Volcanic Complex

The palygorskite of the Volcanic Complex near of Lisbom (Portugal) is particular both in the size of the fibres and in chemical composition. It appears as veins of very pure mineral. From hand specimen and optical observations it can be described as a macroscopic palygorskite. The crystals are large with exfoliation traces of several hundred microns to few millimetres in length. In thin section, this palygorskite is colourless, translucent, negative biaxial, with positive elongation and parallel extinction. The optically homogeneous fibres and laths are shown by the selected area electron diffraction to be composed of aggregates of much thinner fibres rotated differently around the c crystal axis which represents their common elongation direction. The chemical formula obtained by the X-ray EDS is Si8.02O20 (Al1.91 Fe0.04 Mg 2.01) (OH)2 (OH2)4 Ca 0.01 Na 0.07 4(H2O) very close to the ideal formula of a pureMg-Al palygorskite,with almost no octahedral Fe, and noAl in tetrahedral sites. The cell parameters are a0 or a0 sin q = 12.64 A° , b0 = 17.84 A° and c0 = 5.3 A°

Mineralogical and Crystalochemical Characterization of the Sepiolite Deposit from Andrichi (Pranjani Basin, Serbia)

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Smectites: The key to the cost overruns in the construction of the third set of locks of the Panama Canal

The third set of locks of the Panama Canal is one the most impressive civil infrastructures in the world. Its construction, however, was delayed by two years incurring cost overruns in billions that were mainly related to the use of the local basalt as the raw material for concrete production. The rapid degradation during the construction of an apparent sound basalt resulted in the huge loss of fines during the manufacturing of concrete. In the rock, olivine and glass are, respectively, altered to iddingsite and palagonite that are mainly composed of smectites. Smectites are also found around plagioclase and pyroxene crystals and filling the dense network of micro- and nano-cracks. Moreover, these smectites are spatially interconnected, which is the key to explaining the unexpected behavior and the rapid degradation of the basalt. Such a rapid degradation of basic igneous rocks – exposed to the weather and then utilized as a construction material – is not frequent, yet it is significant enough to call for the development of a new standard for the use of these materials in construction

VNIR-SWIR spectroscopic study of samples from the sepiolite-palygorskite polysomatic series

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEConsejería de Educación, Junta de Castilla y Leónpu

Estudio de la microfracturación del basalto de Miraflores (Panamá)

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Mineralogical characterization of the granite of Golpejas (Salamanca)

En el presente trabajo se propone una sistemática de caracterización mineralógica a través de la aplicación de la espectrorradiometría de campo VNIR-SWIR (visible e infrarrojo cercano y de onda corta) para el estudio de caolines. La caracterización mineralógica de base ha sido la Difracción de Rayos X, de acuerdo con la rutina clásica de los estudios de minerales arcillosos. Como caso de estudio, se ha seleccionado el yacimiento de estaño de Golpejas (Salamanca). El yacimiento estannífero de Golpejas está constituido por varias láminas de un microgranito albítico que da lugar a estructuras más o menos circulares, cortando a los metasedimentos del Complejo Esquisto-Grauváquico en la Zona Centro-Ibérica. El emplazamiento tuvo lugar durante la fase extensional de la Orogenia Varisca y los procesos de greisenización y caolinitización hidrotermal aumentaron la concentración de Sn,Ta,Nb, y dieron lugar a la formación de la caolininita por alteración de los feldespatos primarios. Puesto que los minerales del grupo de la caolinita (caolinita,dickita y nacrita) presentan rasgos característicos y diferenciadores en el intervalo de longitudes de onda con la técnica propuesta (VNIR-SWIR), los espectros obtenidos junto con las técnicas clásicas de estudio de minerales arcillosos permiten la caracterización mineralógica del caolín de Golpejas (Salamanca).In the present work, we propose a systematics of mineralogical characterization through field spectrometry VNIR-SWIR (visible, near-infrared and short-wave infrared) as well as the techniques most used for the identification and semiquantification of special clays. The basis of the mineralogical study has been X-ray diffraction, according to the classical routine of studies on clay minerals. As a case of study, the tin deposit of Golpejas (Salamanca) has been selected. The Golpejas tin deposit consists of several sheets of albite microgranite, more or less circular in shape, that intersect the metasediments of the schist-graywacke complex in the Iberian Zone. The emplazament took place during the extensional phase of Variscan Orogeny and the processes of greaseization and hydrothermal kaolinitization increased the concentration of Sn, Nb, Ta as well as kaolin. The albite leucogranite carrying the mineralization show a strong kaolinitization that occurred during the final phase of the mineralizing stage. As kaolinite group minerals (kaolinite, dickite and nacrite) have characteristic and differentiating features in the range of wavelenght studied with the proposed technique (VNIR-SWIR), the spectra obtained together with the classic clay mineral study techniques, allow us the mineralogical characterization of the Golpejas kaolin.Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Caracterización de politipos del grupo de la caolinita mediante difracción de Rayos-X

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

¿Qué es la dickita?

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu