Caracterització i estudi de procedència de l’alabastre del retaule de l’altar major de Poblet

S’ha realitzat la caracterització del material petri usat en l’execució del retaule de l’altar major de Poblet, esculpit en guix alabastrí, des dels punts de vista mineralògic, petrològic i geoquímic, mitjançant l’observació macroscòpica i microscòpica (microscòpia òptica de transmissió electrònica de rastreig) i la difracció de raigs X. Els resultats revelen que aquest alabastre és, en força àrees del retaule, de molt bona qualitat, si bé presenta abundants components que evidencien un descens en la seva puresa en algunes àrees. La caracterització geoquímica d’algunes mostres d’alabastre mitjançant l’estudi de les composicions isotòpiques del sofre i l’oxigen del sulfat del guix, ha permès recolzar analíticament la teoria coneguda documentalment sobre la procedència dels alabastres del retaule de l’altar major de Poblet de la zona de Sarra

Mineralogical Characterization of Dolomitic Aggregate Concrete: The Camarasa Dam (Catalonia, Spain)

The Camarasa Dam was built in 1920 using dolomitic aggregate and Portland cement with two di erent compositions: type A (dolomite and Portland cement) and type B (dolomite and sand-cement). The sand cement was a finely powdered mixture of dolomite particles and clinker of Portland cement. The mineralogy of concrete was studied by optical microscopy, scanning electron microscopy, and x-ray powder di raction. Reaction of dedolomitization occurred in the two types of concrete of the Camarasa Dam, as demonstrated by the occurrence of calcite, brucite, and/or absence of portlandite. In the type A concrete, calcite, brucite, and a serpentine-group mineral precipitated as a rim around the dolomite grains and in the paste. The rims, a product of the dedolomitization reaction, protected the surface of dolomite from the dissolution process. In type B concrete, in addition to dolomite and calcite, quartz and K-feldspar were present. Brucite occurred in lower amounts than in the type A concrete as fibrous crystals randomly distributed in the sand-cement paste. Although brucite content was higher in the type A concrete, type B showed more signs of loss of durability. This can be attributed to the further development of the alkali-silica reaction in this concrete type

Mineralogical characterization of dolomitic aggregate concrete: the Camarasa Dam (Catalonia, Spain)

The Camarasa Dam was built in 1920 using dolomitic aggregate and Portland cement with two different compositions: type A (dolomite and Portland cement) and type B (dolomite and sand-cement). The sand cement was a finely powdered mixture of dolomite particles and clinker of Portland cement. The mineralogy of concrete was studied by optical microscopy, scanning electron microscopy, and x-ray powder diffraction. Reaction of dedolomitization occurred in the two types of concrete of the Camarasa Dam, as demonstrated by the occurrence of calcite, brucite, and/or absence of portlandite. In the type A concrete, calcite, brucite, and a serpentine-group mineral precipitated as a rim around the dolomite grains and in the paste. The rims, a product of the dedolomitization reaction, protected the surface of dolomite from the dissolution process. In type B concrete, in addition to dolomite and calcite, quartz and K-feldspar were present. Brucite occurred in lower amounts than in the type A concrete as fibrous crystals randomly distributed in the sand-cement paste. Although brucite content was higher in the type A concrete, type B showed more signs of loss of durability. This can be attributed to the further development of the alkali-silica reaction in this concrete type.Peer ReviewedPostprint (published version

MINROCIND una eina d'aprenentatge presencial e interactiva dels jaciments de roques i minerals industrials a Catalunya. Eina d'aprenentatge presencial i/o interactiu en el àmbit dels ensenyaments de la mineralogia i petrologia aplicada

Es tracta d'un material i eina didàctica a la vegada. Té doncs una doble vesant: a) una part física constituïda per una mostra de roca polida i una làmina prima de la mateixa roca, per a ser utilitzada a l'hora de pràctiques a classe; i b) una part virtual formada per una base de dades interactiva on els estudiants trobaran fitxes amb les característiques bàsiques de la roca, i la descripció de les pedreres més importants on es troben i la seva importància com a recurs econòmic, com a roca ornamental i/o industrial

Argilitas expansivas de un tunel del tren de alta velocidad (Barcelona-Lerida)

En la zona de Montblanc (Tarragona) se están construyendo unos túneles para el tren de alta velocidad que unirá Lérida con Barcelona. El túnel ha sido construido en los materiales de la depresión del Ebro situados entre la Sierra de Miramar y el límite nor-oriental de la Sierra de Prades

Distribution and speciation of Ni in sepiolite-falcondoite- type 'garnierite' by EXAFS

Ni-laterites represent one of the main Ni sources worldwide, with about 40% of the annual production (Gleeson et al., 2003). A problem in laterites is to find a reliable system to control the exact partitioning of Ni among the different minerals in the lateritic profile, because laterite profiles are generally constituted by fine-grained minerals. The determination of Ni-sorption mechanisms during the process of lateritization arises as a very important target from both the mining and environmental point of view (e.g. RoquéRosell et al., 2010)

Mineralogía del yacimiento laterítico niquelífero San Felipe, Camagüey, Cuba.

El propósito de este estudio fue la caracterización mineralógica y cristaloquímica del perfil de intemperismo del yacimiento San Felipe (Camagüey, Cuba). En este trabajo se exponen resultados de difracción de rayos X (DRX), microscopía óptica, microscopía electrónica de barrido con analizador de dispersión de energía (SEM-EDS) y microscopía electrónica de transmisión con analizador EDX acoplado. Las principales fases minerales portadoras de níquel son esmectitas, lizardita, cloritas, asbolanas, goethita y maghemita. Dentro del grupo de las esmectitas se identificó la nontronita como principal especie mineralógica portadora de la mineralización, representando alrededor del 65% en peso de las menas del horizonte; esta especie fue también caracterizada cristaloquímicamente. Estos resultados podrán ser utilizados para medir el grado de eficiencia industrial en la futura planta de beneficio de San Felipe

Patrones de formación y de alteración de la vermiculita en las carbonatitas volcánicas de Catanda (Angola)

En las proximidades de la localidad de Catanda (Angola) se localiza un conjunto de pequeños edificios volcánicos de composición carbonatítica, desarrollados sobre una depresión de unos 50 Km2 la cual está encajada en granitos del Arcaic

Fe-Ni-bearing serpentines from the saprolite horizon of Caribbean Ni-laterite deposits: new insights from thermodynamic calculations

Fe-Ni-bearing serpentine from the saprolite horizon is the main Ni ores in hydrous silicate-type Ni laterites and formed by chemical weathering of partially serpentinized ultramafic rocks under tropical conditions. During lateritization, Mg, Si, and Ni are leached from the surface and transported downwards. Fe2+ is oxidized to Fe3+ and fixed as insoluble Feoxyhydroxides (mostly goethite) that incorporate Ni. This Ni is later leached from goethite and incorporated in secondary serpentine and garnierite. As a result, a serpentine-dominated saprolite horizon forms over the ultramafic protolith, overlapped by a Fe-oxyhydroxide-dominated limonite horizon. The serpentine from the protolith (serpentine I) is of hydrothermal origin and yields similar Ni (0.10-0.62 wt.% NiO) and lower Fe (mostly 1.37-5.81 wt.% FeO) concentrations than the primary olivine. In contrast, Fe-Ni-bearing serpentine from the saprolite (serpentine II) shows significantly higher and variable Fe and Ni contents, typically ranging from 2.23 to 15.59 wt.% Fe2O3 and from 1.30 to 7.67 wt.% NiO, suggesting that serpentine get enriched in Fe and Ni under supergene conditions. This study presents detailed mineralogical, textural, and chemical data on this serpentine II, as well as new insights by thermodynamic calculations assuming ideal solution between Fe-, Ni- and Mg-pure serpentines. The aim is to assess if at atmospheric pressure and temperature Fe-Ni-bearing serpentine can be formed by precipitation. Results indicate that the formation of serpentine II under atmospheric pressure and temperature is thermodynamically supported, and pH, Eh, and the equilibrium constant of the reaction are the parameters that affect the results more significantly

Relación entre las resistividades y la mineralogía ¿litofacies de explotaciones activas de yeso

El sulfato de calcio, y en particular su fase hidratada, el yeso, es uno de los minerales evaporíticos más frecuentes en la naturaleza y el más abundante en afloramiento, debido principalmente a su menor solubilidad relativa en comparación con el resto de minerales evaporíticos