Chemical composition of celadonite-glauconite minerals and cristobalite from altered oceanic basalts of DSDP Hole 49-407

Features of associations of newly formed minerals in Oligocene basalts from the Reykjanes Ridge (DSDP Hole 407), which consist in wide development of celadonite-glauconite group minerals, as well as saponite, cristobalite and specific Fe-Si formations is shown. Detailed mineralogical and geochemical characteristics of these newly formed minerals are reported. It is firstly shown that at underwater alteration of basalts not only celadonite can be generated, but also glauconite. Dependence of secondary mineral composition from petrochemical features of original basalts and from their permeability is revealed. It is concluded that complexes of secondary minerals formed during alteration of basalts with similar petrochemical characteristics in the ocean and on the continent are different.

Effect of Al2O3 and Cr2O3 on loquidus temperatures in the cristobalite and tridymite primary phase fields of the MgO-"FeO"-SiO2 ststem in equilibrium with metallic iron

The effects of alumina and chromite impurities on the liquidus temperatures in the cristobalite/tridymite (SiO2) primary phase fields in the MgO-FeO-SiO, system in equilibrium with metallic iron have been investigated experimentally. Using high temperature equilibration and quenching followed by electron probe X-ray microanalysis (EPMA), liquiclus isotherms have been determined in the temperatures range 1 673 to 1 898 K. The results are presented in the form of pseudo-ternary sections of the MgO-FeO-SiO, system at 2, 3 and 5 wt% Al2O3, 2 wt% Cr2O3, and 2 wt% Cr2O3+2 wt% Al2O3. The study enables the liquidus to be described for a range of SiO2/MgO and MgO/FeO ratios. It was found that liquiclus temperatures in the cristobalite and tridymite primary phase fields, decrease significantly with the addition of Al2O3 and Cr2O3.

Investigation of inclusions trapped inside Libyan Desert glass by Raman microscopy

Several specimens of Libyan Desert Glass (LDG), an enigmatic natural glass from Egypt, were subjected to investigation by micro-Raman spectroscopy. The spectra of inclusions inside the LDG samples were successfully measured through the layers of glass and the mineral species were identified on this basis. The presence of cristobalite as typical for high-temperature melt products was confirmed, together with co-existing quartz. TiO2 was determined in two polymorphic species, rutile and anatase. Micro-Raman spectroscopy proved also the presence of minerals unusual for high-temperature glasses such as anhydrite and aragonite.

Effect Of Water On Brittle Fracture Of Sio2 By Molecular Dynamics Study

The influence of water on the brittle behavior of beta-cristobalite is studied by means of molecular dynamics (MD) simulation With the TTAM potential. Crack extension of mode 1 type is observed as the crack opening is filled LIP With water. The critical stress intensity factor K-lc(MD) is used to characterize the crack extension of MD simulation. The surface energy of SiO2 covered with layers of water is calculated at temperature of 300 K. Based oil the Griffith fracture criterion, the critical stress intensity factor K-lc(Griffith) is calculated, and it is in good agreement with that of MD simulation. (C) 2008 Elsevier B.V. All rights reserved.

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������������������������������(APCVD)������,���������������������������SIPOS(������������������������)���,���������SIPOS���������������������SIPOS������������,������������������������������,��������������������������������-Cristobalite(���������)������������������������������,���SiO_x(x���2)������������������������������������������,������������������������������������������������������������������������,���������������������������������������������,���x=0���1���2���

Geochemistry, mineralogy, and chemical modeling of the acid crater lake of Kawah Ijen volcano, Indonesia

The Kawah Ijen volcano-with a record of phreatic eruptions-has its 1000 m wide crater filled with a lake that has existed for at least one century. At present, the lake waters are hot (T ��� 37��C), strongly mineralized (TDS = 105 g/L) and extremely acidic (pH ��� 0.4). By its volume, the Javanese lake is probably the largest accumulation in the world of such acidic waters. Mineralogy of the suspended solids within the lake waters suggests that concentrations of Si, Ca, Ti, and Ba are controlled by precipitation of silica, gypsum, anatase, and barite. Lake sediment is composed of chemical precipitates with composition similar to the suspended solids. Thermodynamic calculations predict that the lake waters have reached equilibrium with respect to ��-cristobalite, barite, gypsum, anglesite, celestite, and amorphous silica, in agreement with the analytical observations. Significant concentrations of ferric iron suggest that the current lake waters are fairly oxidized. Sulfides are absent in the water column but are always present in the native S spherules that form porous aggregates which float on the lake. The presence of native S provides direct evidence of more reduced conditions at the lake floor where H2S is probably being injected into the lake. With progressive addition of H2S to the acid waters, native S, pyrite, and enargite are theoretically predicted to be saturated. Reactions between upward streaming H2S-bearing gases discharged by subaqueous fumaroles, and metals dissolved in the acidic waters could initiate precipitation of these sulfides. A model of direct absorption of hot magmatic gases into cool water accounts for the extreme acidity of the crater lake. Results show that strongly acidic, sulfate-rich solutions are formed under oxidizing conditions at high gas/water ratios. Reactions between the acidic fluids and the Ijen andesite were modeled to account for elevated cation concentrations in lake water. Current concentrations of conservative rockforming elements are produced by dissolution of approximately 60 g of andesite per kg of acid solution. Complete neutralization of the acid lake waters by reaction with the wallrock produces a theoretical alteration assemblage equivalent to that observed in volcano-hosted, acid-sulfate epithermal ore deposits. �� 1994.

Spectroscopic techniques for characterizing portuguese glazed ceramics:a contribution to the study of ancient faiences of Coimbra

Tese de doutoramento, F��sica, Universidade de Lisboa, Faculdade de Ci��ncias, 2013

Genesis of the brecciated rocks from mid atlantic ridge hydrothermal systems : Lucky Strike (37��50���N) and Menez Gwen (37��50���N)

Tese de doutoramento, Geologia (Metalogenia), Universidade de Lisboa, Faculdade de Ci��ncias, 2014

Relaci��n de exposici��n a polvos de carb��n, s��lice cristalina y neumoconiosis, en trabajadores de minas de socav��n, Cundinamarca, 2014.

Objetivo: Determinar el nivel de riesgo de la exposici��n por fracci��n respirable a polvo de carb��n y s��lice cristalina y la prevalencia de neumoconiosis en trabajadores de minas de socav��n del departamento de Cundinamarca. M��todos: estudio de corte transversal, en grupos de exposici��n similar (GES) en las minas seleccionadas, el tama��o muestral fue constituido por 11 empresas y 215 trabajadores en donde se realiz�� un muestreo ambiental para medir los niveles de polvo de carb��n y s��lice cristalina. Resultados: La edad promedio del grupo fue de 46��9,5 a��os y g��nero masculino (97,2%), se encontr�� una asociaci��n significativa entre polvo de carb��n y neumoconiosis (p =0,050) y no fue significativa con exposici��n a s��lice cristalina (p = 0,537). El modelo de regresi��n log��stica mostr�� asociaci��n significativa con la escala de nivel de riesgo de carb��n medio (OR=10.4, IC 95%:1.50, 71.41, p=0,02), ajustando con variables significativas como: tama��o de la empresa mediana (OR = 2,67, IC 95%:1.07, 6.66, p=0,04), antig��edad mayor o igual a 30 a��os (OR = 7,186, IC 95%:2.98, 17.29, p=0,001) y habito tab��quico por m��s de un a��o (OR = 4,437, IC 95%:2.06, 9.55, p=0,001) para s��lice cristalina no hubo asociaci��n en el modelo multivariado. Conclusi��n: El riesgo de exposici��n a carb��n de nivel medio est�� relacionado con la prevalencia de neumoconiosis y otros factores adicionales como tama��o de la empresa mediana, antig��edad mayor o igual a 30 a��os y habito tab��quico por m��s de un a��o para los trabajadores de miner��a de socav��n en Cundinamarca. Para los niveles de s��lice cristalina no se encontr�� asociaci��n significativa.

Obten����o de filtro cer��mico a partir da diatomita e casca de arroz carbonizada visando tratamento de efluente t��xtil

The effluents released by the textile industry have high concentrations of alkali, carbohydrates, proteins, in addition to colors containing heavy metals. Therefore, a filter was prepared aiming primarily to the removal of color. In order to prepare this filter, rice hulls and diatomite were used, which have in their structure, basically amorphous hydrated silica. The silica exists in three crystalline forms: quartz, tridymite and cristobalite. In accordance with the above considerations, this study was divided into two stages; the first corresponds to the preparation of the filter and the second to carry out the tests in the effluent/filter in order to verify the efficiency of the color removal. First, the raw material was subjected to a chemical analysis and XRD, and then the diatomite was mixed, via humid, with a planetarium windmill with 20 %, 40 %, 60 % and 80 % of rice husk ash. To the mixture, 5 % carboxymethylcellulose (CMC) was added as a binder at room temperature. The samples were uniaxially compacted into metallic matrix of 0.3 x 0.1 cm�� of area at a pressure of 167 MPa by means of hydraulic press and then sintered at temperatures of 1,000 ��C, 1,200 ��C and 1,400 ��C for 1 h and submitted to granulometry test using laser, linear retraction, water absorption, apparent porosity and resistance to bending, DTA, TMA and XRD. To examine the pore structure of the samples scanning electron microscope (SEM) was used. Also tests were carried out in a mercury porosimeter to verify the average size of the pores and real density of the samples. In the second stage, samples of the effluent were collected from a local industry, whose name will be preserved, located in Igap��, in the State of Rio Grande do Norte - RN. The effluent was first pretreated before filtration and then subjected to a treatment of flotation. The effluent was then characterized before and after filtration, with parameters of color, turbidity, suspended solids, pH, chemical and biochemical oxygen demand (COD and BOD). Thus, through the XRD analysis the formation of cristobalite α in all samples was observed. The best average size of pore was found to be 1.75 μm with 61.04 % apparent porosity, thus obtaining an average 97.9 % color removal and 99.8 % removal of suspended solid

S��ntese de pigmentos cer��micos inorg��nicos nanom��tricos e encapsulados com estrutura core-shell pela rota dos precursores polim��ricos

The present work has as objective the development of ceramic pigments based in iron oxides and cobalt through the polymeric precursor method, as well as study their characteristics and properties using methods of physical, chemical, morphological and optical characterizations.In this work was used iron nitrate, and cobalt citrate as precursor and nanometer silica as a matrix. The synthesis was based on dissolving the citric acid as complexing agent, addition of metal oxides, such as chromophores ions and polymerization with ethylene glycol. The powder obtained has undergone pre-ignition, breakdown and thermal treatments at different calcination temperatures (700 ��C, 800 ��C, 900 ��C, 1000 ��C and 1100 ��C). Thermogravimetric analyzes were performed (BT) and Differential Thermal Analysis (DTA), in order to evaluate the term decomposition of samples, beyond characterization by techniques such as BET, which classified as microporous materials samples calcined at 700 �� C, 800 �� C and 900 �� C and non-porous when annealed at 1000 �� C and 1100 �� C, X-ray diffraction (XRD), which identified the formation of two crystalline phases, the Cobalt Ferrite (CoFe2O4) and Cristobalite (SiO2), Scanning Electron Microscopy (SEM) revealed the formation of agglomerates of particles slightly rounded;and Analysis of Colorimetry, temperature of 700 ��C, 800 ��C and 900 ��C showed a brown color and 1000 ��C and 1100 ��C violet

Rugosidade superficial de ligas com alto conte��do de cobre, em fun����o do aquecimento acima da temperatura de fus��o.

Being the surface roughness a fundamental property in the fit of the castings, it was determined the roughness of 5 high-copper casting alloys, according to the heating over their melting temperature. That way, the specimens made with smooth plastic in the shape of a rectangular plate, 2 mm x 7 mm x 11 mm were invested into a cristobalite investment. After heating and elimination on the plastic, the molds were filled by 3 g of molten alloy, casted in a electrical casting machine at the casting temperature at 25 degrees C and 50 degrees C overheating. The surface roughness was measured in a roughness analyser, Talysurf. As a result, it was verified that there is a variation of surface roughness among the alloys tested, and the heating of the alloys until 50 degrees C over the melting temperature does not interfere in the roughness.

Mineralogy and chemistry of archaeological ceramic fragments from archaeological Dark Earth site in Colombian Amazon

V��rios s��tios arqueol��gicos de Terra Preta Arqueol��gica (TPA) encontrados na floresta Amaz��nica Colombiana tamb��m cont��m alto conte��do de fragmentos cer��micos semelhantes aqueles da Amaz��nia Brasileira, como mostra o s��tio Quebrada Tacana. Seus fragmentos cer��micos s��o amarelo a cinza, exibem matriz argilosa calcinada envolvendo fragmentos de cariap��, carv��o e part��culas de cinza, gr��os de quartzo e micas. A matriz �� composta de metacaulinita a material amorfo, quartzo, folhas de micas, clorita e sepiolita. Cariap�� e cauixi s��o constitu��dos de cristobalita, da mesma forma o carv��o e as cinzas. Embora n��o detectados pela difra����o de raios x, os fosfatos devem estar presentes, pois foram detectados teores de P2O5 de at�� 2,90 %, possivelmente como fosfatos de alum��nio, j�� que o conte��do de Ca est�� abaixo 0,1 %, o que elimina a possibilidade da presen��a de apatita. Estas caracter��sticas mineral��gicas e qu��micas permitem relacionar estes fragmentos cer��micos com aqueles encontrados nos s��tios de TPA no Brasil e refor��a o f��sforo como um importante componente qu��mico, originado pelo contato dos vasos cer��micos com os alimentos do cotidiano dos povos amaz��nicos pr��-hist��ricos.

The mineralogy and chemistry of the German and Portuguese tiles used to face a historic building in the Amazon region and their natural susceptibility to tropical weathering

As proeminentes edifica����es da cidade de Bel��m foram revestidas durante o s��culo 19 com azulejos produzidos em Portugal e Alemanha que j�� apresentam distintos graus de degrada����o. O Palacete Pinho �� uma das mais importantes destas edifica����es e foi selecionado para se investigar a a����o do clima tropical amaz��nico sobre a degrada����o destes azulejos. Para atingir estes objetivos mapearam-se os azulejos desta edifica����o visando identificar as modifica����es de origem org��nica e inorg��nica e coletas de amostras para an��lises. Os minerais foram determinados por DRX, a composi����o qu��mica por m��todos cl��ssicos ��midos e MEV/SED e os micro-organismos por microscopia. Os resultados obtidos mostram que os azulejos Portugueses e Alem��es s��o distintos entre si. Enquanto o biscoito �� composto de SiO₂ e Al₂O₃, CaO foi encontrado apenas nos Portugueses. Os baixos conte��dos de Na₂O e K₂O indicam adi����o de materiais para redu����o da temperatura de fus��o. SiO₂ e PbO comp��em o vidrado, j�� CoO e FeO foram adicionados como pigmentos. O biscoito dos azulejos Alem��es �� constitu��do de quartzo, mullita e cristobalita, ao contr��rio do Portugu��s com quartzo, gehlenita, diops��dio, calcita e feldspatos. Os vidrados s��o amorfos ao DRX. As diferen��as qu��micas e mineral��gicas entre os azulejos Portugueses e Alem��es indicam que foram produzidos por mat��ria prima distinta, bem como processo termal. As altera����es relacionadas com o intemperismo s��o as finas camadas de detritos (nos Alem��es), manchas de oxida����o, manchas escuras, descolamento do azulejo (no Portugu��s); perda de vidrado e biscoito tornando-se pulverulento como consequ��ncia do estabelecimento de Cyanophyta e bacillariophyta (Portugu��s). As distintas fei����es de degrada����o dos azulejos refletem as suas diferen��as mineral��gicas e qu��micas expostas ao clima tropical Amaz��nico.