Search results for "clay minerals"
showing 10 items of 77 documents
From Maya Blue to “Maya Yellow”: A Connection between Ancient Nanostructured Materials from the Voltammetry of Microparticles
2011
The yellow hue of a series of samples from wall paintings in several Mayan archaeological sites can be attributed to the presence of indigoid compounds, including isatin and dehydroindigo, attached to palygorskite, a local phyllosilicate clay. SEM/EDX, TEM, UV/Vis spectroscopy, and voltammetry of microparticles show that the ancient Mayas could prepare indigo, Maya Blue, and "Maya Yellow" during successive stages. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Chemical weathering of volcanic rocks at the island of Pantelleria, Italy: Information from soil profile and soil solution investigations
2007
Abstract Concentrations of major, minor and trace elements were determined in soil profiles and soil solutions from the island of Pantelleria, Sicily Channel, to evaluate the weathering extent of soils evolved on trachytic and pantelleritic rocks and the aqueous transport of elements by their soil solutions. The chemical index of alteration (CIA) indicates a low-to-moderate degree of weathering; consistently, the mineralogical and geochemical imprints of the parent rocks are generally preserved. The chemical weathering appears to be incongruent, owing to primary minerals and glass dissolving to a variable degree while secondary minerals have formed. Based on the calculated saturation state …
Over-estimation of efficiency of weathering in tropical “Red Soils”: its importance for geoecological problems
2000
Abstract Weathering and soil formation rates are regarded as the main criteria of a tolerable soil loss. The efficiency of weathering in the seasonal semiarid tropics has often been greatly over-estimated especially in the geomorphologic literature in which weathering is assumed to be as fast or even faster than surface erosion. Six selected “Red Soils” in two intramontane basins of hyperthermic SW Nepal near the border with India, with 1500–1750 mm annual rainfall (5 humid months), and a “Black Soil” near Baroda, Gujarat, India (3–4 humid months) were studied mineralogically. Two of the “Red Soils” have TL ages between 10 and 30 ka, the “Black Soil” has one of about 10 ka. The yellowish si…
Clay minerals, oxyhydroxide formation, element leaching and humus development in volcanic soils
2008
Aweathering sequence with soils developing on volcanic, trachy-basaltic parent materials with ages ranging from 100–115,000 years in the Etna region served as the basis to analyse and calculate the accumulation and stabilisation mechanisms of soil organic matter (SOM), the transformation of pedogenic Fe and Al, the formation and transformation of clay minerals, the weathering indices and, by means of mass-balance calculations, net losses of the main elements. Although the soils were influenced by ash depositions during their development and the soil on the oldest lava flow developed to a great extent under a different climate, leaching of elements and mineral formation and transformation co…
Distribution of rare earth elements in marine sediments from the Strait of Sicily (western Mediterranean Sea): Evidence of phosphogypsum waste contam…
2010
Concentrations of rare earth elements (REE), Y, Th and Sc were recently determined in marine sediments collected using a box corer along two onshore–offshore transects located in the Strait of Sicily (Mediterranean Sea). The REE + Y were enriched in offshore fine-grained sediments where clay minerals are abundant, whereas the REE + Y contents were lower in onshore coarse-grained sediments with high carbonate fractions. Considering this distribution trend, the onshore sediments in front of the southwestern Sicilian coast represent an anomaly with high REE + Y concentrations (mean value 163.4 lg g 1) associated to high Th concentrations (mean value 7.9 lg g 1). Plot of shale-normalized REE + …
Role of clays in protecting adsorbed DNA against X-ray radiation
2004
The X-ray emission of the young Sun was much harder and intense than today and might have played a significant role in the evolution of complex organics in protoplanetary environments. We investigate the effects of soft X-rays on tryptophan molecules in aqueous solutions at room temperature. As results of the irradiation experiments we detect several light species indicative of fragmentation, together with large molecular structures such as tryptophan dipeptide and tripeptide. Complexification is more evident in H2O solution than in D2O, probably due to isotopic effects. The abundances of peptides depend on the irradiation dose and decrease with increasing energy deposition. Radicals such a…
Chemical variations in clay minerals of the Archaean Barberton Greenstone Belt (South Africa)
1996
Abstract Four rock profiles of shales, carbonates and greywacke-type sediments were sampled from the mafic compositional influenced sedimentary Fig Tree Group and from overlying, more felsic related, sedimentary Moodies Group of the Archaean Barberton Greenstone Belt in South Africa. Clay separates of forty sedimentary rocks were examined by XRD and SEM to study the mineralogical, chemical and morphological variations of the constitutive illite and chlorite. The clay minerals showed a significant K-enrichment in the illites and Mg- and Fe-depletions in the chlorites upwards the stratigraphic sequence. Three independent parameters influenced these variations: (1) a change in the origin of th…
Structure-related geochemical (REE) and isotopic (K-Ar, Rb-Sr, δ18O) characteristics of clay minerals from Rotliegend sandstone reservoirs (Permian, …
1999
Abstract Euhedral illite cementing the gas-bearing sandstone reservoirs of the Rotliegend in the Niedersachsische rift system (northern Germany) was studied along a horst-to-graben cross-section to examine its chemical and isotopic characteristics. The data show that differentiated illite particles grew during a tectono-thermal event marked by distinct episodic hydrothermal activities along fault drains and in the poral space of sandstones at 210 Ma and at 195 to 190 Ma in horst positions, at 185 to 175 Ma in the nearby graben, and at 170 to 165 Ma in both the horst and graben. Varied REE distribution patterns and initial 87Sr/86Sr ratios (from 0.7124 to 0.7142) relative to illite-particle …
Burial and thermal evolution of the Sicilian fold-and-thrust belt: preliminary results from the Scillato wedge top basin (central-northern Sicily, It…
2016
Wedge top basins are key elements for unravelling the tectonic evolution of fold-and-thrust belts. In detail, their thermal signature and sedimentary fill records modes and time of exhumation of their edges. The Scillato basin is a wedge-top basin located in the central-northern sector of the Sicilian fold-and-thrust belt (western sector of the Madonie Mts). Upper Serravallian-upper Tortonian succession composed by up to 1,200 m thick delta-river to open marine siliciclastic sediments, fills the basin. This succession lies on a deformed substrate made up of thrust sheets composed of Numidian Flysch, Sicilidi and Imerese units stacked with a SW tectonic transport. The basin fill records a po…
Selenium and heavy metals content in some Mediterranean soils
2010
Abstract The study of metal contents in industrial, agricultural or/and polluted soils compared with natural or unpolluted soils is currently necessary to obtain reference values and to assess soil contamination. Nonetheless, very few works published appear in international journals on elements like Se, Li and Sr in Spanish soils. This study determines the total levels of Se, Li, Sr, As, Cd, Co, Cr, Cu, Ni, Pb, V, Zn, Fe, Mn and Ba in 14 natural (unpolluted) soils (Gypsisols, Leptosols, Arenosols and Acrisols), 14 agricultural soils (Anthrosols, Fluvisols and Luvisols), and 4 industrial–urban affected-surface soil horizons (Anthrosols and Fluvisols) of Eastern Spain. The geochemical baselin…