Quimismo de un sedimento clástico formador de esmectita y sus implicaciones en la transformación esmectita-ilita

3 páginas, 1 figura.-- Trabajo presentado en la XX Reunion de la Sociedad Española de Mineralogía, La Coruña (2000).Prior to the development of "in-situ" analysis techniques, data on the chemical composition of minerals was derived exclusively from whole rocks using monomineral samples or from assemblages in which the separation of minerals was possible. Therefore, knowledge concerning the real composition of smectites in soils and sediments was significantly delayed, and it was assumed that the typical smectite composition was that of materials in which they were the only phase or easily separated. Recently, Analytical Electron Microscopy (AEM) analyses have demonstrated that smectites forming sediments or sedimentary rocks can also be analysed in spite of their small size and their defective nature. Smectites play an important role in the geological cycle. They are the basic material for the smectiteillite transformation during the diagenesis of sedimentary materials giving rise to illitebearing sedimentary rocks.Financial support was supplied by Research Project nº PB96-1383 of the Spanish Ministry of Education and Research Group RNM-0179 of the Junta de Andalucía.Peer reviewe

Quimismo de un sedimento clástico formador de esmectita y sus implicaciones en la transformación esmectita-ilita

3 páginas, 1 figura.-- Trabajo presentado en la XX Reunion de la Sociedad Española de Mineralogía, La Coruña (2000).Prior to the development of "in-situ" analysis techniques, data on the chemical composition of minerals was derived exclusively from whole rocks using monomineral samples or from assemblages in which the separation of minerals was possible. Therefore, knowledge concerning the real composition of smectites in soils and sediments was significantly delayed, and it was assumed that the typical smectite composition was that of materials in which they were the only phase or easily separated. Recently, Analytical Electron Microscopy (AEM) analyses have demonstrated that smectites forming sediments or sedimentary rocks can also be analysed in spite of their small size and their defective nature. Smectites play an important role in the geological cycle. They are the basic material for the smectiteillite transformation during the diagenesis of sedimentary materials giving rise to illitebearing sedimentary rocks.Financial support was supplied by Research Project nº PB96-1383 of the Spanish Ministry of Education and Research Group RNM-0179 of the Junta de Andalucía.Peer reviewe

Understanding Surface Processes on Mars Through Study of Iron Oxides/Oxyhydroxides: Clues to Surface Alteration and Aqueous Processes

We are performing oxidation and reduction reactions on hydrated ferric oxide minerals in order to investigate how these might alter under a variety of conditions on the surface of Mars. Preliminary experiments on ferrihydrite and goethite showed that heating these minerals in a dry oxidizing environment produces fine-grained hematite, while heating these minerals in a reducing environment produces fine-grained magnetite. Under Mars-like oxidation levels this magnetite then oxidizes to maghemite. These reactions are dependent on the presence of water and organic material that can act as a reductant. We are using reflectance and Mossbauer spectroscopy to characterize the reaction products and TEM to analyze the sample texture. Our preliminary results indicate that magnetite and maghemite could be formed in the soil on Mars from ferrihydrite and goethite if organics were present on early Mars

The effect of dry grinding on antigorite from Mulhacen, Spain

8 páginas, 9 figuras, 4 tablas.Alteration of the crystal structure of Mulhacén antigorite caused by dry, vibration grinding was investigated by X-ray diffraction (XRD), infrared spectroscopy (IR), thermal analyses (TG), grainsize distribution, and transmission and analytical electron microscopy (TEM, AEM). Grinding for 1 min reduces particles to a size ideal for IR and TG. With prolonged grinding, XRD and electron diffraction patterns showed that the crystal structure was affected mainly along the c axis, causing a partial loss of crystallinity. TG analyses revealed that vibration grinding modified mineral dehydration, accelerating the dehydroxylation process and transforming the structural OH to adsorbed water in the resulting matrix. IR spectra and AEM showed that grinding affected the tetrahedral sheet to a lesser extent than tlie octahedral sheet. Partial release of Mg by preferential destruction of the octahedral sheet after 10 rnin grinding produced an increase in the Si/Mg ratio iil semi-crystalline particles, whereas the anlorphous material product after 120 min showed the same composition as the initial antigorite. TEM and grain-size distribution results revealed that grinding led to a general decrease in particle size at the beginning of the experiment followed by the agglomeration of ultrafine particles as grinding proceeded.Financial support was supplied by Research Project PB96- 1383 of the Spanish Ministry of Education and Research Group RNM-0179 of the Junta de Andalucía.Peer reviewe

Chemical composition of smectites formed in clastic sediments. Implications for the smectite-illite transformation

14 páginas, 5 figuras, 4 tablasAnalytical electron microscopy of representative smectites from soils and sediments revealed that K was present in significant proportions. It was the major interlayer cation in soils from pelitic rocks, continental and marine sediments, independent of their diagenetic grade. Sodium was predominant only in soils from basic rock. Fluvial sediments contained smectites with both kinds of interlayer compositions. The octahedral composition of each sample ranged widely, covering various fields of dioctahedral smectites. The most important trend was the substitution of Al by Fe and Mg; the chemistry of each smectite particle was determined by the parent mineral from which it formed. The real interlayer composition has important implications for the diagenetic smectite-illite transformation. When considering a typical K content, the smectite-illite reaction, with chlorite and quartz as subproducts, needs only 0.21 K atoms. For more K-rich compositions, a reaction is possible without an external supply of K.Proyecto de investigación PB96-1383 del Ministerio de Educación e Investigación y el Grupo de Investigación RNM-0179 de la Junta de Andalucía.Peer reviewe

Alteración experimental de una roca subvolcánica con una solución 1 M NaOH

3 páginas.-- Trabajo presentado en la XX Reunion de la Sociedad Española de Mineralogía, La Coruña (2000).Smectites are widely distributed over the earth's crust as the weathering products of volcanic glasses or rock-forming minerals. They have been synthesised at low temperature using various starting materials. On the other hand, berthierine is commonly considered to be typical of marine sediments, undoubtedly as a result of its frequent occurrence in marine oolitic ironstone formations. But, there are still few experimental works dealing with its formation. Because most syntheses of clays were carried out using synthetic starting materials under hydrothermal conditions, the aim of the present study is the formation of clay minerals from a subvolcanic rock during its interaction with 1 M NaOH solution at room temperature.Financial support was supplied by Research Project nº PB96-1383 of the Spanish Ministry of Education and Research Group RNM-0179 of the Junta de Andalucía.Peer reviewe

Experimental clay-mineral formation from a subvolcanic rock by interaction with 1 M NaOH solution at room temperature

15 páginas, 12 figuras, 4 tablasThe alteration process of a subvolcanic rock with calcic plagioclase, pyroxene, and olivine as major components was investigated by X-ray diffraction (XRD) and analytical and transmission electron microscopy (TEM/AEM). Experimental interaction with 1 M NaOH solution led to the formation of dioctahedral beidellite to Fe-rich montmorillonite after 1 and 3 d of reaction. This range of smectite composition is similar to that from natural subvolcanic-derived soil formed from the same parent material. After 14 d of reaction, a berthierine-smectite (B-S) interstratified clay had partially replaced the smectite. Although, the presence of smectite interlayers prevented analysis of pure berthierine, berthierine-rich B-S interstratifications have a composition similar to pure berthierine. After 40 d, the alteration process led to a 7-Å S interstratifications whose composition falls between greenalite and lizardite. A series of amorphous materials were also found in the 14 and 40-d experiments. The most abundant of these is a Si-Ca-Fe-rich material, whose chemical composition approaches that of the starting rock. In contrast, two other amorphous materials had a smectitic composition.Proyecto de investigación BTE2000-0582 del Ministerio de Educación e Investigación y el Grupo de Investigación RNM-0179 de la Junta de Andalucía.Peer reviewe

Degradation of antagorite under dry grinding

2 páginas. Resumen de la comunicación presentada en el Congreso de Mineralogía y Petrología SEM98 y XVIII Reunión de la SEM (Bilbao, 3-6 octubre 1998)Peer reviewe