Sand Mineralogy Research Articles

Reserva mineral de potássio em Latossolo cultivado com Pinus taeda L.

No Brasil, aproximadamente 1,87 milhões de hectares são plantados com as espécies de Pinus, normalmente em solos pobres quimicamente. Os objetivos deste trabalho foram estudar a mineralogia das frações areia, silte e argila e estimar a reserva mineral de K por diferentes métodos de extrações químicas em solo naturalmente pobre nesse nutriente e cultivado com Pinus taeda L., no Segundo Planalto Paranaense. Foram selecionadas cinco árvores com maior diâmetro (árvores dominantes), em uma área de 500 m², para abertura de uma trincheira (1,6 m) na projeção da copa de cada árvore. Todos os perfis foram classificados como Latossolo Vermelho-Amarelo distrófico típico e apresentaram similaridade na morfologia e na sequência dos horizontes, cujas profundidades médias foram: O = 0,04 m, A1 = 0-0,09 m, A2 = 0,09-0,24 m, BA = 0,24-0,43 m, B1 = 0,43-0,66 m e B2 = 0,66-1,60+ m. As amostras coletadas em cada horizonte foram submetidas a análises físicas (granulometria) e químicas (pH, carbono orgânico, acidez potencial, Al3+ e bases trocáveis, P disponível, K total e não trocável), e as frações areia, silte e argila foram estudadas por difratometria de raios-X (DRX). As frações areia e silte dos solos apresentaram mineralogia bastante uniforme, com predomínio absoluto de quartzo e apenas ocorrência de discretas reflexões de mica por DRX. A fração argila também apresentou limitada ocorrência de minerais micáceos. Os tratamentos sequenciais para remoção de óxidos de Fe, gibbsita e caulinita foram eficientes para concentração de mica na fração argila, o que facilitou a identificação de biotita e muscovita por DRX. Os baixos teores de K não trocável obtidos com diferentes concentrações de HNO3 fervente (máximo de 91 mg kg-1) e de K total extraído com HF concentrado (máximo de 202,7 mg kg-1) foram consistentes com a pobreza das frações do solo em minerais primários, fontes desse nutriente. As correlações positivas e significativas entre os teores não trocáveis de K no solo e os teores e conteúdos do nutriente nas árvores indicaram a importância de formas de reservas do nutriente na nutrição da espécie em solos altamente intemperizados e pobres em K trocável.

Influence of gradation on shear strength and volume change behavior of silty sands

The results of an experimental program regarding the effects of gradation on shear strength and volume change behavior of silty sands are presented. Consolidated drained direct shear tests were performed on two clean base sands and twelve silty sands obtained by mixing those base sands with two different non-plastic silts at various fines contents ( 25%). Drained shear strengths were observed to be not significantly influenced by either base sand gradation or silt gradation or fines content for the studied range. Increasing fines content has increased the volumetric contraction of specimens at similar void ratio. However, the amount of increase in volumetric contraction of silty sands were found to be affected by silt gradation when other influencing factors such as fines content, base sand gradation and mineralogy were kept the same. Moreover, the amount of increase in volumetric contraction of silty sands were also found to be affected by base sand gradation when other influencing factors such as fines content, silt gradation and mineralogy were kept the same.

Effects of full-scale beach renovation on fecal indicator levels in shoreline sand and water

Recolonization of enterococci, at a non-point source beach known to contain high background levels of bacteria, was studied after a full-scale beach renovation project. The renovation involved importation of new exogenous sand, in addition to infrastructure improvements. The study's objectives were to document changes in sand and water quality and to evaluate the relative contribution of different renovation activities towards these changes. These objectives were addressed: by measuring enterococci levels in the sand and fecal indicator bacteria levels (enterococci and fecal coliform) in the water, by documenting sediment characteristics (mineralogy and biofilm levels), and by estimating changes in observable enterococci loads. Analysis of enterococci levels on surface sand and within sediment depth cores were significantly higher prior to beach renovation (6.3–72 CFU/g for each sampling day) when compared to levels during and after beach renovation (0.8–12 CFU/g) (P < 0.01). During the renovation process, sand enterococci levels were frequently below detection limits (<0.1 CFU/g). For water, exceedances in the regulatory thresholds that would trigger a beach advisory decreased by 40% for enterococci and by 90% for fecal coliform. Factors that did not change significantly between pre- and post- renovation included the enterococci loads from animals (approx. 3 × 1011 CFU per month). Factors that were observed to change between pre- and post- renovation activities included: the composition of the beach sand (64% versus 98% quartz, and a significant decrease in biofilm levels) and loads from direct stormwater inputs (reduction of 3 × 1011 CFU per month). Overall, this study supports that beach renovation activities contributed to improved sand and water quality resulting in a 50% decrease of observable enterococci loads due to upgrades to the stormwater infrastructure. Of interest was that the change in the sand mineralogy also coincided with changes in biofilm levels. More work is needed to evaluate the relationships between beach sand mineralogy, biofilm characteristics, and the retention of fecal indicator bacteria in sand.

Soil Mineralogy of Forest Soils of Chamoli District, Uttarakhand

Soil properties and sand mineralogy were studied in forest area of Chamoli district of Uttarakhand covering four forest divisions namely Badrinath Forest Division, Kedarnath Wildlife Forest Division, Nanda Devi National Park and Alaknanda Soil Conservation Forest Division with different ranges viz. Chamoli, Joshimath, Gopeshwar, Madhya Pindari, Paschim Pindari, Naraingarh, Dhanpur, Attagad, Nandprayag and Pipalkoti. The study area was selected on the basis of altitude, vegetation distribution, parent material and topography. The forest type of the area is Himalayan moist temperate forests with Picea smithiana, Cedrus deodara, Quercus leucotrichophora, Pinus roxburghii, and Miscellaneous (Amaltas, Rohani, Asain, Semal and Mahua) as the dominant species. Geologically, the rocks of the study area are pre-cambrian to early paleozoic in age with recent and subrecent deposits. The soils were generally sandy loam in texture with acidic pH. Organic carbon is generally higher in forest areas at high altitude with maximum accumulation in the surface layer. Cation exchange capacity of the soil in different depth showed inconsistent trend. Exchangeable Ca2+and Mg2+ increased in the sub-surface horizons in some of the profiles due to presence of limestone parent material. The study suggested that P. smithiana grows well on schist and gneiss, C. deodara flourishes well on limestone, dolomite and quartzite, Q. leucotrichophora flourishes with good regeneration on phyllite and slate, P. roxburghii grows on quartzite and limestone and miscellaneous forests on boulders, limestone, shales, pebbles. Mineralogical composition showed that variations are mostly due to nature of parent rock and weathering stage. The study, therefore, indicates the presence of low to moderate amounts of weatherable minerals suggesting their podzolic nature.

Pendugaan Perkembangan Alfisols di Kecamatan Jatipuro, Karanganyar Dengan Model Kestabilan Genetik

Title : The Development Prediction and Differentiated Alfisols at Jatipuro Sub District of Karanganyar with Genetic Stability Model. This research had been conducted at Jatipuro, Sub district of Karanganyar from July until September, 2007. The aim of this research are to know and comparing the development of Alfisols with genetic stability model. This research was descriptive‐explorative research, and the variables approached by field’s survey and supported by laboratory analysis. The site sampling on the fields determined with soil mapping unit. Samples for physical, chemicals and sand mineralogy properties was take from representative pedon or profile from each soil mapping unit. This research uses statistical analysis stepwise regression to know which the most variable can explain the soil development, and the Eberhart‐Russell’s genetic stability model to determine the degree of soil stability for any soil mapping unit. The result of this research can be concluded that the 3rd soil mapping unit (NGEPUNGSARI series, Ultic Hapludalfs, very fine, kaolinitic, active, non acid, isohyperthermic family) was the most’s stable in soil development, and followed by 1st soil mapping unit (JATISOBO series, Vertic Hapludalfs, very fine, kaolinitic, active, non acid, isohyperthermic family). Even though, the 2nd soil mapping unit (JATISUKO series, Typic Hapludalfs, very fine, kaolinitic, active, non acid, isohyperthermic family) was the most’s unstable in soil development. Each soil mapping unit also showed the difference of soil development, that looking from the endogen and exogen’s factors can be explained. Keywords: Alfisolfs, development, differentiated, Genetic Stability Model

Mineralogy of Nigerian Bituminous Sands using Particle Induced X-ray Emission (PIXE) Spectrometry

Mineralogy of Nigerian Bituminous Sands using Particle Induced X-ray Emission (PIXE) Spectrometry

Soil Mineralogical Investigations in Different Forest Stands of Nainital Forest Division, Uttarakhand

Mineralogy of fine sand and clay fractions at different locations in natural forests representing varied type of forest vegetation, parent material and altitude in Nainital, Ramgarh and Bhawali Range of Nainital Forest Division Uttarakhand was investigated. Light minerals constituted bulk of fine sand fractions and comprised quartz, feldspar and mica in order of their abundance. Heavy minerals contributed very small fraction and were dominated by opaque minerals followed by biotite, calcite, chloritized mica, garnet, zircon etc. The study suggests that quartz, tourmaline, opaque minerals and rutile were the resistant minerals. The most weatherable minerals were feldspar, biotite, mica, calcite, chloritized mica, hornblende etc. Clay fractions are characterized by micas and illite as the dominant clay mineral associated with appreciable amount of kaolinite and chlorite. The small amount of mixed layer silicate mineral, vermiculite, montimorillonite are also present in the clay fractions of these soils. Mineralogical composition showed that variations are mostly due to nature and composition of parent rock and degree of weathering stage. The study, therefore, indicates the presence of low to moderate amount of weatherable minerals suggesting their podzolic nature.

Sedimentological and geochemical evidence for multistage failure of volcanic island landslides: A case study from Icod landslide on north Tenerife, Canary Islands

[1] Volcanic island landslides can pose a significant geohazard through landslide-generated tsunamis. However, a lack of direct observations means that factors influencing tsunamigenic potential of landslides remain poorly constrained. The study of distal turbidites generated from past landslides can provide useful insights into key aspects of the landslide dynamics and emplacement process, such as total event volume and whether landslides occurred as single or multiple events. The northern flank of Tenerife has undergone multiple landslide events, the most recent being the Icod landslide dated at ∼165 ka. The Icod landslide generated a turbidite with a deposit volume of ∼210 km3, covering 355,000 km2of seafloor off northwest Africa. The Icod turbidite architecture displays a stacked sequence of seven normally graded sand and mud intervals (named subunits SBU1–7). Evidence from subunit bulk geochemistry, volume, basal grain size, volcanic glass composition and sand mineralogy, combined with petrophysical and geophysical data, suggests that the subunit facies represents multistage retrogressive failure of the Icod landslide. The basal subunits (SBU1–3) indicate that the first three stages of the landslide had a submarine component, whereas the upper subunits (SBU4–7) originated above sea level. The presence of thin, non-bioturbated, mud intervals between subunit sands suggests a likely time interval of at least several days between each stage of failure. These results have important implications for tsunamigenesis from such landslides, as multistage retrogressive failures, separated by several days and with both a submarine and subaerial component, will have markedly lower tsunamigenic potential than a single-block failure.

Drivers of bacterial diversity dynamics in permeable carbonate and silicate coral reef sands from the Red Sea

Permeable sediments and associated microbial communities play a fundamental role in nutrient recycling within coral reef ecosystems by ensuring high levels of primary production in oligotrophic environments. A previous study on organic matter degradation within biogenic carbonate and terrigenous silicate reef sands in the Red Sea suggested that observed sand-specific differences in microbial activity could be caused by variations in microbial biomass and diversity. Here, we tested this hypothesis by comparing bacterial abundance and community structure in both sand types, and by further exploring the structuring effects of time (season) and space (sediment depth, in/out-reef). Changes in bacterial community structure, as determined via automated ribosomal intergenic spacer analysis (ARISA), were primarily driven by sand mineralogy at specific seasons, sediment depths and reef locations. By coupling ARISA with 16S-ITS rRNA sequencing, we detected significant community shifts already at the bacterial class level, with Proteobacteria (Gamma-, Delta-, Alpha-) and Actinobacteria being prominent members of the highly diverse communities. Overall, our findings suggest that reef sand-associated bacterial communities vary substantially with sand type. Especially in synergy with environmental variation over time and space, mineralogical differences seem to play a central role in maintaining high levels of bacterial community heterogeneity. The local co-occurrence of carbonate and silicate sands may thus significantly increase the availability of microbial niches within a single coral reef ecosystem.

Petrography, mineralogy, and geochemistry of deep gravelly sands in the Eyreville B core, Chesapeake Bay impact structure

– The ICDP–USGS Eyreville drill cores in the Chesapeake Bay impact structure reached a total depth of 1766 m and comprise (from the bottom upwards) basement-derived schists and granites/pegmatites, impact breccias, mostly poorly lithified gravelly sand and crystalline blocks, a granitic slab, sedimentary breccias, and postimpact sediments. The gravelly sand and crystalline block section forms an approximately 26 m thick interval that includes an amphibolite block and boulders of cataclastic gneiss and suevite. Three gravelly sands (basal, middle, and upper) are distinguished within this interval. The gravelly sands are poorly sorted, clast supported, and generally massive, but crude size-sorting and subtle, discontinuous layers occur locally. Quartz and K-feldspar are the main sand-size minerals and smectite and kaolinite are the principal clay minerals. Other mineral grains occur only in accessory amounts and lithic clasts are sparse (only a few vol%). The gravelly sands are silica rich (∼80 wt% SiO2). Trends with depth include a slight decrease in SiO2 and slight increase in Fe2O3. The basal gravelly sand (below the cataclasite boulder) has a lower SiO2 content, less K-feldspar, and more mica than the higher sands, and it contains more lithic clasts and melt particles that are probably reworked from the underlying suevite. The middle gravelly sand (below the amphibolite block) is finer-grained, contains more abundant clay minerals, and displays more variable chemical compositions than upper gravelly sand (above the block). Our mineralogical and geochemical results suggest that the gravelly sands are avalanche deposits derived probably from the nonmarine Potomac Formation in the lower part of the target sediment layer, in contrast to polymict diamictons higher in the core that have been interpreted as ocean-resurge debris flows, which is in agreement with previous interpretations. The mineralogy and geochemistry of the gravelly sands are typical for a passive continental margin source. There is no discernible mixing with marine sediments (no glauconite or Paleogene marine microfossils noted) during the impact remobilization and redeposition. The unshocked amphibolite block and cataclasite boulder might have originated from the outer parts of the transient crater.

Mineral and Bacterial Diversities of Desert Sand Grains from South-East Morocco

Mineralogy and microbiology of sand from Merzouga (Morocco) were simultaneously characterized, with the purpose of contributing to a better understanding of the geomicrobiology of deserts. In spite of very low measured bacterial biomass, bacterial diversity on each of the five defined mineralogical classes, was found high. An original grain by grain cultivation method enabled to obtain bacterial isolates with an unusually high recovery rate. The results of this study show that the genus Arthrobacter is well adapted to this environment with a preference for grains other than the dominant mineral quartz, and that the genera Chelatococcus and Saccharotrix are strongly attached to the grains.

Holocene ooids of Aitutaki Atoll, Cook Islands, South Pacific

Although oolitic sands are widespread throughout the Phanerozoic carbonate rock record, and they are abundant in some modern shallow-marine carbonate systems, recent ooids have not been recognized from any locality in the Pacific Basin. On Aitutaki Atoll (Cook Islands, South Pacific), oolitic sands occur in water depths of 2.1–6.3 m within the lagoon and, less abundantly, on shallower reef aprons. Most ooids are between 150 and 300 μm in diameter, have between 1 and 25 concentric to irregular laminae, and occur with peloids and skeletal grains. Cortical laminae include Mg-calcite crystals with radial, tangential, and random orientations. The occurrence and distribution of oolitic sands on Aitutaki are facilitated by a convergence of hydrodynamic and chemical factors. Wave-driven currents, combined either with flow separation over a sharp increase in depth at the reef apron–lagoon interface or with oceanward flow in the lee of islands, serve to transport ooids without flushing them from the system. Here, pH, alkalinity, and carbonate supersaturation are at some of the highest levels in the tropical Pacific. The restricted occurrence of Holocene oolitic sands in areas of the Pacific and Atlantic Basins with elevated pH and total alkalinity reflects the importance of carbonate saturation thresholds in limiting the spatial distribution of these sands in modern shallow-marine settings. These recent examples are consistent with interpretations of the importance of these variables in determining the distribution, abundance, and cortical mineralogy of oolitic sands throughout the Phanerozoic stratigraphic record of carbonate accumulation.

CARACTERIZAÇÃO QUÍMICA, FÍSICA E MINERALÓGICA DE ESTÉREIS E REJEITO DA MINERAÇÃO DE FERRO DA MINA DE ALEGRIA, MARIANA-MG

In the area under the Alegria iron mine influence (Mariana, Minas Gerais, Brazil), samples of fours materials were collected, identified as phyllite, soil, overburden rock, and mine spoil, for chemical, physical, and mineralogical characterization. All four materials are poor in plant macro and micronutrients, presenting low amounts of organic carbon and physical characteristics which hinder the development of plant root system. The high bulk density and particle density values of all materials are related to the presence of heavy minerals, mainly Fe oxides. Except for phyllite, which presented considerable amounts of silt, the materials presented high amounts of sand: more than 50%. As far as water retention is concerned, the phyllite showed the highest retention but it could be detrimental to plant growth due to excess of water and surface sealing. The mineralogy of sand, silt, and clay fractions is basically constituted by goethite, hematite, and quartz, while phyllite presents, besides these minerals, kaolinite, microcline, gibbsite, and mica. KEY-WORDS: Iron mining; mineralogical characterization; iron mine spoil.

Atributos mineralógicos de três solos explorados com a cultura do melão na Chapada do Apodi: RN

Este trabalho teve o objetivo de caracterizar os principais solos explorados com a cultura do melão na Chapada do Apodi, Estado do Rio Grande do Norte, no tocante aos aspectos mineralógicos, visando fornecer subsídios para implantação de um manejo adequado à cultura e ao solo. Foram selecionados três solos: Cambissolo Háplico Ta eutrófico típico - CXve (Typic Haplocambids), Latossolo Vermelho-Amarelo eutrófico argissólico - LVAe (Typic Eutrotorrox) e Argissolo Vermelho distrófico arênico - PVd (Arenic Kandiustults). Foram realizadas análises mineralógicas nas frações areia, silte e argila, por difratometria de raios X, além de estudos complementares em amostras indeformadas por meio da microscopia eletrônica de varredura. A composição mineralógica é semelhante nos perfis estudados; o quartzo predomina nas frações areia e silte, enquanto a fração argila é constituída predominantemente por caulinita. O perfil 1 (CXve), comparado com os outros dois, é o menos evoluído na escala pedogenética. Os perfis 2 (LVAe) e 3 (PVd) apresentam praticamente a mesma maturidade, embora o primeiro seja um pouco mais evoluído. O fato de o perfil 1 (CXve) apresentar química de solo jovem e mineralogia de solo muito evoluído revela incoerência entre os atributos químicos e mineralógicos daquele solo. Pelas condições de semi-aridez do local em que os três perfis estão inseridos, o domínio da caulinita na fração argila sugere que os solos foram originados em condições climáticas diferentes das atuais, provavelmente mais úmidas, ou que eles tenham se desenvolvido a partir de um material pré-intemperizado.

Mineralogical study of some arsenic contaminated soils of West Bengal, India

Five arsenic affected soil profiles, one each from Ghentugachhi and Gotera village of Chakdah block, Gayeshpur, Kalyani block, Nadia district; Ramnagar village of Baruipur block and Sonarpur mouza of Sonarpur block of South 24 Parganas district of West Bengal, India covering the soils of Typic Haplustepts, Typic Endoaquepts, Vertic Haplustepts and Aquic Haplustepts respectively have been studied for their detail mineralogical, chemical composition and also to know the level of arsenic contamination and their probable source. These soils are very deep, developed on Alluvium and are under rice, vegetable and guava cultivation. Sand mineralogy data of these soils are dominated by opaque and limonite, whereas silt is mainly constituted of micas followed by kaolinite and chlorite. The clay mineralogy of the soils indicates that smectite is in higher proportion in Ghentugachhi and Gotera soils followed by mica, kaolinite, chlorite and vermiculite and in the other soils, mica is the dominant clay mineral. In some of these soils, the interstratified mixed layer minerals are also present. The mineralogy class for the soils of Ghentugachhi, Gayeshpur, Baruipur is ‘mixed’ and for Gotera and Sonarpur it is ‘illitic’. Differential thermal analysis (DTA) of clay fraction of surface soil of the profiles displayed the presence of the minerals like magnetite, marcasite, arsenopyrite, illite, montmorillonite and quartz. The source of arsenic in these soils are probably due to the presence of arsenic bearing minerals, marcasite and arsenopyrite, and also it may occur as adsorbtion on iron hydroxide coated sand grains and clay minerals. Arsenic concentration is very high in the surface horizon of pedon 2 (20.2 mg kg − 1 ) and it shows a decreasing trend down the subsurface horizon. The higher concentration of arsenic in the surface horizon may be due to higher abundance of opaque minerals, limonite, and marcasite.

Mineralogy and phase transition of oil sands coke ash

Coke obtained from Syncrude and Suncor was investigated to characterize the metals and minerals by ashing it at various temperatures. Samples were collected by high temperature ashing at 100 °C intervals from 400 to 1200 °C. Samples were also obtained from low temperature ashing (LTA) which gives little effect on the mineral assemblage compared to HTA samples. X-ray diffraction patterns of Suncor and Syncrude coke ash were analyzed qualitatively and quantitatively to characterize the mineral phases in the sample and their thermal transition behavior. In Suncor ash, kaolinite, illite, gypsum, anhydrite, microcline, anorthite, hematite, sillimanite and quartz were dominant phases in ash from the LTA temperature up to 700 °C, and mullite, cristobalite, hercynite, albite, anorthite, pseudobrookite and other iron–titanium oxides were dominant mineral phases from 700 to 1200 °C. In Syncrude ash, illite, anhydrite, quartz, anorthite, microcline, sillimanite and hematite were dominant up to 700 °C, and hercynite, anorthite, albite, pseudobrookite and other iron–titanium oxides were dominant up to 1200 °C. The higher quantities of Ca, K and Na, and the lower quantities of V, Fe and Ni in Syncrude ash resulted in higher amorphocity and the different mineral phases.

LANDFILL AND NATURAL SOILS ON THE SOMMA-VESUVIUS VOLCANIC COMPLEX, ITALY

The aims of this investigation were to study the modifications induced by a landfill activity on native soil morphology and properties, and to highlight the critical environmental issues related to this activity in a volcanic environment. We studied the soils from a solid waste disposal activity on Somma-Vesuvius volcanic complex. The disposal site was in operation for about 50 yr, and was recently dismantled. Adjacent natural soils were also selected and investigated. The natural soils were derived from superimposition of pyroclastics deposited by the volcanoes Somma-Vesuvius and Phlegrean Fields. In these soils, andic soil properties were mainly detected in the subsoils, while vitrandic characteristics distinguished the upper soils. Little or no pedogenetic development characterized the human-influenced soils that consisted of chaotic masses of Vesuvian earthy materials and sparse or interbedded garbic material. The earthy materials had physical and chemical characteristics similar to those of the natural upper soil horizons, lacked andic soil properties, and had a sand mineralogy similar to that of natural upper soils. Environmental concerns came out of the presence of garbage in coarse textured and weakly developed soil materials overlaying the permeable aquifer characterizing the studied area. The studied human-influenced soils were arranged using U.S. soil taxonomy into the Vitrandic subgroup of Xerorthents, that also identified the natural soils. This class was inadequate for interpreting the soil morphology and properties of soils from the solid waste disposal site, and the related environmental issues. Therefore, the suitability of adopting Garb-classes is discussed.

Óxidos de ferro das frações areia e silte de um Nitossolo desenvolvido de basalto

Foi estudada a composição mineralógica dos óxidos de ferro das frações areia, silte e argila de cinco amostras coletadas de um perfil de um Nitossolo Vermelho desenvolvido de basalto toleítico, localizado próximo a Tupaciguara (18 º 35 ' 33 '' S; 48 º 42 ' 18 '' O), na região do Triângulo Mineiro, Minas Gerais. Porções de areia e de silte foram submetidas à separação magnética e a ataques químicos seletivos com NaOH 5 mol L-1 e com uma mistura ditionito-citrato-bicarbonato, com o objetivo de identificar os principais óxidos de ferro magnéticos e suas associações mineralógicas. Maghemita (fórmula ideal, gFe2O3) foi o único mineral magnético identificado nas frações areia e silte; não foi encontrada evidência de ocorrência de magnetita nessas frações. Os resultados Mössbauer apenas sugerem a co-existência de mais de um tipo cristaloquímico de maghemita, na fração areia, embora não sejam claramente separáveis dos espectros Mössbauer obtidos sem campo magnético aplicado. A fase magnética mais rica em Al tem fórmula média, deduzida de resultados de microssondagem eletrônica, Fe2,36(2)3+ Al0,24(2)3+ Ti0,06(3)4+ Ä0,341(1) O4 (Ä = vacância catiônica). A ilmenita férrica detectada de dados Mössbauer na porção magnética da fração silte corresponde a uma solução sólida xFe2+Ti4+O3(1-x)Fe2(3+)O3, com x » 0,83. São discutidas algumas dificuldades e alternativas de interpretação dos resultados Mössbauer, como os do presente caso, em que ocorrem contribuições espectrais simultâneas de hematita e maghemita.

Mineralogia e fontes de potássio em solos no Rio Grande do Sul cultivados com arroz irrigado

Estudos desenvolvidos com arroz irrigado por inundação no estado do Rio Grande do Sul têm evidenciado ausência de resposta desta cultura à adubação potássica, mesmo em solos com baixo teor de potássio disponível. Este trabalho objetivou verificar a contribuição da mineralogia destes solos como fonte potencial de potássio para a cultura do arroz. Para tal, selecionaram-se quatro solos representativos das zonas orizícolas do estado do Rio Grande do Sul (Planossolo Hidromórfico, Planossolo Háplico, Gleissolo Háplico e Chernossolo Ebânico) cultivados com arroz irrigado. Estes solos apresentam baixos teores de potássio trocável e não apresentam respostas à adubação potássica. Nas amostras dos horizontes A e B dos quatro solos, foram analisadas a granulometria e a composição química. A mineralogia das frações areia, silte e argila foi identificada por difratometria de raios-X. Os principais minerais fontes de potássio foram os seguintes: na fração areia, feldspatos e micas; nas frações silte e argila, feldspatos, micas, esmectitas e esmectitas com hidróxi-alumínio entrecamadas. A quantidade de potássio total, nas frações granulométricas, diferiu entre os solos. As frações silte e argila apresentaram os maiores teores de K-total, exceto para o Planossolo Háplico, que revelou maior reserva de potássio na fração areia. A ausência, ou a baixa resposta, à adubação potássica na cultura do arroz irrigado nesses quatro solos pode ser explicada pelos minerais fontes de potássio que ocorrem nesses solos.

Mineralogy, stratigraphy, and provenance of soil coverbeds in the Kumara district, Westland

The sand and silt mineralogy of four soils preserved on fluvioglacial outwash terraces at Kumara indicates that the main soil body is developed in up to 1 m of loessial coverbeds that accumulated subsequent to cessation of gravel terrace formation. Oxygen isotope abundances of the dominant mineral quartz in these soils show a higher temperature origin for the >250 |4.m fraction, consistent with derivation from local granodiorites. Finer quartz is of a mixed provenance origin consistent with the variety of rock types in the region. The finest quartz, <5 Jim, of aerosolic origin, can be used as a proxy time record for the coverbed accumulations. The widespread 22 590 yr BP Aokautere Ash chronohorizon is preserved in three of the profiles, whilst wind redeposition of the glass shards is responsible for traces of rhyolitic glass in all subsequent horizons. Widespread landscape erosion is postulated either immediately before or during deposition of the K‐l terrace, so that similar subsequent coverbed sequences are preserved on the K‐1 and all older terraces in this district. Magnetic mineral assemblages in the profiles indicate a slightly different loessial provenance for the Cockeye, K‐l, and K‐2.1 profiles, but the K‐2.2 is significantly different from the rest. This is probably a function of aeolian winnowing and variability of source materials. In the past, different mountain catchments have connected with different lower river reaches, due to transcurrent movement on the Alpine Fault. This is interpreted as having led to changing provenance of river sediment supplying loess to local soils.