Principal Clay Minerals Research Articles

Pozzolanic reactions of six principal clay minerals: Activation, reactivity assessments and technological effects

Six standard clays, before and after calcination at 3 or 4 temperatures and being mixed with Ca(OH)2 [CH] in the presence of simulated cement pore solution, and with ordinary Portland cement, respectively, were studied in detail. Chemical compositions of most clays conform well to the requirement in ASTM C 618. Water demand of clay-containing mortar varies, depending on the crystal chemistry of raw clays, and on the specific surface area of calcined clays. Measurements of XRD background or alkali soluble Si are rapid methods in evaluation of the pozzolanic activity of clays. Compressive strength of mortars based on the raw clays is affected by structure of clays. Calcination increases the pozzolanic activity of clays and the compressive strength of the Portland cement — clay mortars. A close correlation exists between compressive strength of mortars and particle size distribution of the dehydroxylated clays. The most common reaction products of clay — CH mixtures are C-S-H2 and C4AHx, while C2ASHj8 and C3AH6 were also detected with clays rich in Al.

Magnesium-Rich Clays of the Meerschaum Mines in the Amboseli Basin, Tanzania and Kenya

AbstractThe Sinya Beds of the Amboseli Basin in Tanzania and Kenya consist largely of carbonate rocks and Mg-rich clays that are intensely deformed where exposed in and near former meerschaum mines. The carbonate rocks consist of limestone and dolomite in Tanzania, but only dolomite has been identified in Kenya. Sepiolite and mixed-layered kerolite/stevensite (Ke/St) are subordinate constituents of the carbonate rocks. The carbonate rocks and overlying bedded sepiolite were deposited in a semiarid lake basin at the foot of the large volcano Kilimanjaro. Calcite and dolomite of the carbonate rocks have δ18O values 4–6‰ lower than calcite and dolomite of the late Pleistocene Amboseli Clays, suggesting that the Sinya Beds were deposited in the middle or early Pleistocene under a different climatic regime when meteoric water had lower δ18O values than at present.Mg-rich clay minerals form veins and fill cavities in the Sinya Beds. The principal clay minerals are sepiolite and Ke/St, some of which contains substantial Al and Fe (Al-Ke/St). NEWMOD® modeling and other X-ray diffraction (XRD) data suggest that most of the Ke/St contains 25–50 percent kerolite layers, but minor amounts of kerolite-rich Ke/St are present in some samples. Illite with an inferred high content of Fe or Mg is a minor constituent of the samples with Al-Ke/St. The cavity-filling clays were chemically precipitated, as shown by field relationships and SEM study. The early-deposited clays of veins and cavities are principally Ke/St with minor sepiolite, and the latest clay is sepiolite (meerschaum), generally with minor Ke/St.The δ18O values of cavity-filling Ke/St range from 22.5–25.6‰ and correlate with mineral composition, with the highest values associated with the highest content of stevensite and the lowest values with the highest content of kerolite. This relation suggests that high salinities favored stevensite and low salinities favored kerolite. δ18O values of sepiolite (meerschaum) fall in the middle of the range for Ke/St, suggesting that salinity was not the main control on sepiolite precipitation. High values of aSiO2/aMg2+ may have been a major factor in sepiolite precipitation.Different mixtures of dilute ground water and saline, alkaline lake water in pore fluids may largely account for the differences in clay mineralogy of cavity-filling clays. Sepiolite is the dominant clay mineral in lacustrine sediments of the Amboseli Basin, and the cavity-filling sepiolite may reflect a high proportion of lake water. The low-Al Ke/St may have formed from fluids with a higher proportion of ground water. Detrital clay was very likely a factor in forming the Al-Ke/St, for which δ18O values suggest a saline environment.

CLAY-MINERAL STUDIES OF THE SUBSURFACE NIGER DELTA

Mineralogical studies of Tertiary subsurface sediments in the Niger Delta have shown that smectite, kaolinite, mixed-layer illite/smectite and illite are the principal clay minerals, with subordinate quantities of chlorite. Clays from the Recent delta have similar mineralogical compositions.

The geological significance of manganese distribution in Jurassic-Cretaceous rocks of the Pindos Basin, Peloponnese, Greece

The Jurassic-mid-Cretaceous Radiolarite Series of the Pindos zone of the Peloponnese is a deep-water sediment sequence. It comprises Jurassic red mudstones, siliceous mudstones and ribbon-bedded cherts; and Cretaceous red mudstones, siliceous mudstones, cherts, calc-turbidites and terrigenous turbidites. Bedded manganese ores occur both in cherty calc-turbidites and ribbon-bedded cherts. In order to determine the origin of Mn enrichment, the transition element geochemistry and mineralogy has been determined for sediment samples from seven representative sections of the Radiolarite Series, representing an along and across strike section of the Pindos basin. Smectite and palygorskite are the principal clay minerals, with lesser mica, sepiolite and chlorite. Fe Al ratios in Jurassic rocks are close to values in continental detritus but increase upwards to the middle Cretaceous. Nevertheless, the association of volcanic rocks with Jurassic sediments is circumstantial evidence that the minor Mn enrichment is the result of hydrothermal processes. The hypothesis that high Fe Al in Cretaceous sediments is due to ophiolitic detritus is untenable in the Peloponnese, where sediment is derived from sources lacking ophiolites: the Fe enrichment must therefore result from hydrothermal processes, which may be related to formation of oceanic crust in the Pindos-Arvi zones. Mn concentrations are associated with diagenetic cherts at the top of calc-turbidites; in these settings, Mn correlates positively with Ca and negatively with Fe, suggesting that the concentration of beds of ore is diagenetic.

Composition and origin of some calcrete deposits in south Western Desert of Egypt

The examined calcretes outcropping at southwestern Egypt are mainly developed on the Cretaceous Nubian sandstones. They are morphologically classified as hardpan type, and geologically described as valley calcretes. Twelve calcrete and six Nubian samples were petrographically, mineralogically and chemically examined. Their heavy mineral constituents were also studied. Data obtained showed that our calcretes consist mainly of low Mg-calcite and quartz with minor quantities of feldspar and gypsum. The principal clay mineral identified in the clay fractions are kaolinite and palygorskite, associated with minor amounts of illite/smectite mixed layer, illite and smectite. These clay minerals are partly detrital inherited from the original sediments and partly authigenic developed during the calcrete formation. Comparisons with the chemistry of both Egyptian coastal and world calcretes show that the studied calcrete is low in CaO, MgO and P 2O 5 and is highly enriched in SiO 2, Al 2O 3, K 2O and TiO 2 contents. The examined trace elements are largely detrital in origin and their distribution is mainly controlled by the contents of quartz, clays, carbonate and iron oxides.

EFFECT OF POTASSIUM REMOVAL BY CROPS ON TRANSFORMATION OF ILLITIC CLAY MINERALS

We studied the effect of K+ fertilizer application on the transformation of clay minerals in soils from long-term field experiments and exhaustive cropping pot experiments. Soils used were alluvium, gray-brown, and brown soils with illite as the principal clay mineral. X-ray diffraction analysis of soil samples revealed that cropping without K+ fertilizer application had led to a substantial decrease in illite content and to an increase of smectite and interstratified illite/smectite minerals. In the alluvium soil containing carbonate, stabile smectite formed, probably because of the high soil pH, whereas in the other soils with lower pH, degradation of illite resulted in the formation of interstratified illite/smectite minerals. Illite degradation was especially intensive in the <0.06-μm and <0.2-μm particle size fractions. We suggest that the removal of K+ by plants resulted in a depletion of interlayer K+ in illite followed by the degradation of the clay mineral. Pot experiments with clover and ryegrass showed that the K+ uptake of the crop from the nonexchangeable fraction (interlayer K+) was quantitatively related to the increase in the dry K+-fixation capacity of the soil.

Reservoir Quality, Sediment Source, and Regional Aspects of Norphlet Formation, South State Line Field, Greene County, Mississippi: ABSTRACT

South State Line field, discovered in 1970, is centrally located in the productive Jurassic Norphlet trend of the eastern Gulf Coast. The Norphlet Formation at South State Line has produced gas and condensate from normally pressured eolian sandstones at depths of more than 17,900 ft (5455 m). The 600-ft- (183-m) thick Norphlet Formation is composed of 100% sandstone and consists of two reservoir types: a poorer quality upper sandstone having low permeability (0.6 md) and a good-quality lower sandstone with better permeability (15.5 md). The upper sandstone exhibits tighter compaction of framework grains and more cement than the lower sandstone. Significantly, the upper sandstone contains authigenic illite (which promotes pressure solution), whereas the lower sandstone contains authigenic chlorite (which inhibits cementation and possibly pressure solution). On a regional scale, illite is the principal diagenetic clay mineral in the western area of the Norphlet trend (Mississippi to Texas), whereas chlorite is the principal diagenetic clay mineral in the east (Alabama to Florida). Not surprisingly, reservoir quality is poorer in the western portion of the trend. A comparison of framework grains in the upper and lower sandstones shows no significant compositional differences. Both are mature arkosic sandstones with a transitional-continental source (easternmore » Appalachians). No evidence was seen of a quartz-rich Ouachita or cratonic source. Volcanic and plutonic rock fragments are slightly more abundant in the lower sandstone, possibly reflecting a shifting of compositional terranes within a single source area along the eastern side of the Appalachians. The lower Norphlet sandstone may have been derived from Triassic volcanics, whereas the upper sandstone may have been derived from a more metamorphic source.« less

Clay mineral burial diagenesis: A case study from the Calabar flank of the Niger Delta

Detailed clay mineralogic and chemical analyses of Tertiary subsurface sediments of the Agbada and Akata Formations, from two wells on the Calabar Flank of the Niger Delta, have been systematically studied with a view to understanding clay mineral burial diagenesis. Five principal clay minerals, smectite, illite, kaolinite, chlorite and various proportions of mixed-layer illite/smectite were identified. Seven major oxides (SiO 2, Al 2O 3, MgO, Fe 2O 3, CaO, Na 2O, K 2O) were analysed for with an atomic absorption spectrophotometer, with a view to ascertain any depth related variations. The geothermal gradient of the two wells (Uruan-1 and Uda-1) was also calculated. The results appear to suggest a transformation from smectite to a mixed-layer illite/smectite (I/S) phase. The transformation first goes to a random I/S phase, and then to ordered I/S and back to random I/S, even though postulated conditions for a complete transformation to illite did exist. It would therefore seem, from this case study, that neither temperature nor the availability of potassium is the principal factor controlling the transformation. Kaolinite and chlorite distribution does not exhibit any systematic trend that could be related to burial diagenesis. These results provoked an extensive literature review on the subject, and key ideas discerned are summarized here. The prognosis? In the author's opinion, we still have a lot to learn about the factors that control the mechanics and reaction extent of clay mineral burial diagenesis.

地熱帯の粘土鉱物と産状

The formation temperature of principal clay minerals from geothermal fields has been estimated using reported data on temperatures measured in drillholes as well as homogenization temperatures of alteration minerals. In this case, only the data from very active wells with an activity index of 100 or nearly 100 were used. As a result, smectite will form at temperatures below 200°C, regular rlixed-layers of chlorite-smectite and micasmectite at a range from 200 to 220°C, chlorite from 220 to 325°C, K-mica from 245 to 325°C, and biotite above 325°C. These stability relations are considered to be principally temperature dependent, and therefore can be used as a geothermometer.

The causes and effects of aging in quick clays

The physicochemical properties of a clay from La Baie, Quebec were found to be typical of Champlain quick clays: very low plasticity, liquidity index greater than 3, sensitivity greater than 500, and pH of about 9.5. The mineralogy is characterized by the abundance of primary or "rock flour" minerals such as feldspar, quartz, amphibole, and calcite, with illite as the principal clay mineral. The pore water chemistry consists predominantly of sodium bicarbonate. Low concentrations of sulfate, calcium, and magnesium and high alkalinity and pH are attributed, in part, to anaerobic sulfate-reduction processes taking place in situ.Quick clay samples stored in the laboratory showed signs of aging regardless of the storage procedure. The remoulded strength and the liquid limit increased with time, whereas the sensitivity, the liquidity index, and the pH decreased. The water content, plastic limit, and undisturbed strength remained practically unchanged. The pore water concentrations of calcium, magnesium, and sulfate increased by severalfold.The aging phenomenon is attributed, for the most part, to the oxidation of iron sulfide, which results in the formation of iron hydroxide and sulfuric acid. The production of acid causes the dissolution of calcium carbonate, which increases the concentration of divalent cation in the clay, thereby reducing interparticle repulsion and increasing the remoulded strength. The oxidation of organic matter, resulting in the formation of carbonic acid, also contributes to the aging by its effect on the solubility of calcium carbonate. Key words: aging, chemical reactions, physicochemical phenomena, sensitivity, time effects.

The Precursor of the Cretaceous-Tertiary Boundary Clays at Stevns Klint, Denmark, and DSDP Hole 465A

Results of detailed mineralogical, chemical, and oxygen isotope analyses of the clay minerals and zeolites from two Cretaceous-Tertiary (K/T) boundary regions, Stevns Klint, Denmark, and Deep Sea Drilling Project (DSDP) Hole 465A in the north central Pacific Ocean, are presented. In the central part of the Stevns Klint K/T boundary layer, the only clay mineral detected by x-ray diffraction is a pure smectite with > 95 percent expandable layers. No detrital clay minerals or quartz were observed in the clay size fraction in these beds, whereas the clay minerals above and below the boundary layer are illite and mixed-layer smectite-illite of detrital origin as well as quartz. The mineralogical purity of the clay fraction, the presence of smectite only at the boundary, and the delta(18)O value of the smectite (27.2 +/- 0.2 per mil) suggest that it formed in situ by alteration of glass. Formation from impact rather than from volcanic glass is supported by its major element chemistry. The high content of iridium and other siderophile elements is not due to the cessation of calcium carbonate deposition and resulting slow sedimentation rates. At DSDP Hole 465A, the principal clay mineral in the boundary zone (80 to 143 centimeters) is a mixed-layer smectite-illite with >/=90 percent expandable layers, accompanied by some detrital quartz and small amounts of a euhedral authigenic zeolite (clinoptilolite). The mixed-layer smectite-illite from the interval 118 to 120 centimeters in the zone of high iridium abundance has a very low rare earth element content; the negative cerium anomaly indicates formation in the marine environment. This conclusion is corroborated by the delta(18)O value of this clay mineral (27.1 +/- 0.2 per mil). Thus, this mixed-layer smectite-illite formed possibly from the same glass as the K/T boundary smectite at Stevns Klint, Denmark.

Geochemical and sedimentological studies of a box core from the western sector of the Peru Basin

The distribution of sediments, micronodules and manganese nodules which has been studied in a number of cores from the Peru Basin is clearly related to the proximity of the basin to the C.C.D. and to the equatorial high-productivity zone. One core from the Peru Basin has been looked at in considerable detail. In this core an extensively bioturbated calcareous, siliceous-rich upper sedimentary unit is underlain by an “overconsolidated” dark brown clay. Characteristic differences in mineralogy and chemistry are observed in the composition of these sediment types with the dark brown clays having higher contents of Mn, Fe, Co, Ni, Cu, Zn and P than the sediments of the upper horizon. In addition, these dark brown clays contain montmorillonite as the principal clay mineral whereas the sediments of the upper-sediment horizon consist of montmorillonite, kaolinite and illite. Micronodules are much more abundant in the coarse fraction (> 40 μm) of the dark brown clay horizon than in the upper sedimentary unit and are characterized by higher Mn Fe ratios and higher Ni and Cu contents than those from the upper-sediment horizon. This reflects the fact that these “overconsolidated” sediments are well oxidized and that element remobilization from the micronodules has not taken place within this sediment type. In the upper sedimentary unit there is a sharp drop in the Mn Fe ratio and Ni and Cu contents of the micronodules immediately beneath the sediment surface, reflecting the selective migration of Mn and other transition elements such as Ni and Cu from the micronodules. Buried managanese nodules are found at two horizons within the sediment column. These nodules show characteristic differences in their surface texture compared to surface nodules, but no marked difference in composition. The buried nodules are not associated with any well-defined feature such as a sedimentary hiatus. It is suggested that nodules are maintained at the sediment surface by bioturbation. Buried nodules are simply those nodules that have failed to be maintained at the sediment—water interface.

Analcimic zones in the tertiary of anatolia and their geological positions

The Anatolian Tertiary and especially the Neogene have some geological series with analcime as the principal rock-forming mineral. Sedimentation basins receiving material in suspension and in solution permit the authigenesis of analcime dolomite, calcite and opal(C-T). Analcimes formed by hydrothermal alteration on the ocean floor, after the pillow lava and diabasic dyke complexes of ophiolites, can form a source of detrital analcime when they are on the continental medium. Continental alteration of the pillow lavas and diabasic dykes permits the formation of solutions suitable in composition for analcime authigenesis. Analcimes formed in these environments are particularly related to the silica content of these media. Principal clay minerals formed with analcimic formations are smectites and (14 s—14 c) mixed layers. Illite, chlorite and corrensite are also present in smaller quantities.

Modern sediments and sedimentary processes in Lake Rudolf (Lake Turkana) eastern Rift Valley, Kenya

ABSTRACTTertiary sediments around Lake Rudolf (now Lake Turkana) in the East African Rift Valley have yielded abundant palaeontological and palaeoanthropological remains. The present study provides a basis for interpreting the ancient lake environment and furthering our knowledge of rift valley lacustrine deposits.Bottom sediments in Lake Rudolf are fine‐grained (average 71% clay) well laminated and have montmorillonite, kaolinite and illite as the principal clay minerals. The sediments are relatively poor in silica (40–45%) but rich in Fe2O3 (10%). Both mineral proportions and chemical composition change systematically over the area of the lake and delineate four sedimentological provinces: (1) iron‐rich, silty kaolinitic muds (Omo Delta); (2) iron‐rich, fine‐grained montmorillonite muds (North Basin); (3) silty montmorillonite muds rich in Na2O and K2O (Central Delta); and (4) argillaceous calcite silts (South Basin). Omo Delta and North Basin sediments are derived from the volcanics of the Ethiopian plateau; the source of Central Delta sediments is the Precambrian metamorphic terrain of the rift valley margin; the South Basin has a restricted detrital input.The water in the lake is alkaline (pH 9.2) and moderately saline (TDS = 2500 p.p.m.). Comparisons with influent water from the Omo River indicate a 200‐fold concentration for the lake water. Models based on equilibrium between sediments and water column account for most of the non‐conservative chemical components in the lake water.Sedimentation rates are high (about 1 m per 1000 years) and the dominance of detrital sediments makes Lake Rudolf unusual in comparison with other closed‐basin lakes in the African Rift Valley although some similarities with ancient rift valley deposits are suggested.

Comparative study of the fixation of inorganic mercury on the principal clay minerals and the sediments of the Loire Estuary

Samples of kaolinite, illite, and montmorillonites were agitated with solutions of mercuric chloride at different salinities, clay turbidities, and concentrations of mercuric ions. The rates of adsorption and maximum quantities adsorbed were obtained in terms of these factors. Clays with known quantities of adsorbed mercury were agitated with fresh and salt water to measure rates of desorption. The values obtained are compared with an analysis of the water and sediments of the Loire Estuary, based on a large number of samples taken over the period 1972–1975. Mercury pollution has considerably decreased over this period.

Clay minerals as an index of the degree of metamorphism of the carbonate and terrigenous rocks in the South Wales coalfield

ABSTRACTIllite, illite‐montmorillonite (I‐M) mixed layer, kaolinite and chlorite are the principal clay minerals identified in the carbonate and terrigenous carboniferous rocks in the South Wales coalfield. Mineralogic changes and illite crystallinity are the main modifications in the studied rocks. Progressive illitization of I‐M mixed layers (decrease in their expandabilities) towards the western part of the coalfield (i.e. in the direction of increase in coal‐rank and grade of metamorphism), and the development of vermicular kaolinite, dickite, allevardite and pyrophyllite in the anthracite area are the main mineralogic changes. Illite crystallinity was determined by Weaver's sharpness ratio (S.R.) and isosharpness ratio maps of illite in the carbonate and terrigenous rocks are produced showing a gradual increase in illite crystallinity towards the west. Illites in the terrigenous rocks tend to be aluminous (evidenced by the increase in their intensity ratios, ‘I.R.’) with increase in coal‐rank and grade of metamorphism towards the west. These changes are controlled to some extent by lithology. Correlation of illite S.R. with either its I.R. or expandability of I‐M mixed layer, has outlined two diagenetic zones in the coalfield: zone I, the Diagenetic zone, in the eastern and southern regions; and zone II, the Metadi‐agenetic zone, covering the central and northern parts of the central region. The Anchimetamorphic zone (zone III), which corresponds to the anthracite area in the northwestern region, was differentiated by correlating the illite S.R. with coal‐rank. The occurrence of the above mentioned diagenetic zones and modifications of the clay minerals in the carboniferous rocks of the South Wales coalfield are mainly lateral without variation with increase in depth.

Soil-sized eolian dusts from the lower troposphere of the eastern Mediterranean Sea

Soil-sized eolian dusts have been collected by a mesh technique from the lower troposphere of the eastern Mediterranean. The overall average dust-loading in this region is 14 μg m −3 of air, which is among the highest recorded for maritime soil-sized dusts. There are two distinct dust populations in the eastern Mediterranean; these have been termed the “northeastern Mediterranean assemblage” and the “southeastern Mediterranean assemblage”. The dusts of the “northeastern assemblage” originate in the soils of southern Europe. The average dust-loading of this assemblage is 12 μg m −3 of air, and illite is the principal clay mineral with secondary amounts of kaolinite and the smectites. These dusts make only a secondary contribution to the land-derived material in the underlying deep-sea sediments. The dusts of the “southeastern assemblage” have their origin in the desert belts of North Africa and the Middle East. Their average dust-loading is 17 μg m −3 of air, and kaolinite is their dominant clay mineral. Dusts of the “southeastern assemblage” make an important contribution to the land-derived fractions of some eastern Mediterranean deep-sea sediments. In addition to eolian dusts, river-transported material from the island of Cyprus has also been investigated. The effects of this “Cyprus assemblage” on sedimentation in the eastern Mediterranean is confined to the immediate vicinity of the island itself.

Shelf sediments of the Ganges delta with special emphasis on the mineralogy of the western part, Bay of Bengal, Indian Ocean

Shelf sediments at the mouth of the Hooghly River which forms the western part of the Ganges—Brahmaputra delta consist of sands, silts and clays and their various admixtures. The bulk of the sediments consists of moderately sorted fine sand to very fine sand. There is variation in lithology in the vertical and horizontal directions, as revealed from the study of the grab and core samples collected in this area, suggesting growth of the delta in different stages. In most of the samples three populations have been recognised. The grain-size variation has resulted from mixing of a number of different grain-size populations. A detailed study of the heavy minerals indicates that the suite consists of hornblende, tremolite/actinolite, opaques, zircon, pyroxenes (ortho-and clino-), garnet, sillimanite, chlorite, muscovite, biotite, epidote, monazite, kyanite, staurolite, riebeckite, carbonates and glauconite. The assemblage and the distribution patterns suggest two distinct mixed igneous and metamorphic sources for the sediments—the Himalayas to the north, mainly drained by the Ganges—Brahmaputra and their tributaries, and the peninsular shield drained by the Dhamra and other easterly-flowing rivers debouching into the Bay of Bengal. The mineralogy of the core samples in the top and bottom layers does not differ, indicating that the source area remained the same during the time of deposition of the sediments. The mineralogy of the sediments in this area, when compared with the mineralogy of the Deep-Sea Drilling Project site in the Bengal fan situated very far to the south, shows similarity because the sediments of the Ganges are carried to the deep-sea. Depending on the mineral assemblage, the area has been divided into four distinct zones: (1) Hooghly River province, consisting of hornblende, tremolite/actinolite, epidote and garnet; (2) a mixed province characterised by epidote, monazite, zircon, kyanite, staurolite, hornblende, tremolite/actinolite, biotite; (3) Dhamra River province characterised by opaques, sillimanite and orthopyroxene; (4) an offshore province comprising muscovite, chlorite and pyroxene. ILlite and kaolinite are the principal clay minerals in the sediments. The mineralogical, grain size and the lithologic studies of the sediments from the core samples suggest a southward to south-southwestward direction of dispersals of the sediments in the eastern part of the area.

Eolian dust from the lower atmosphere of the eastern Atlantic and Indian Oceans, China Sea and Sea of Japan

Dust-loadings in the lower atmosphere of the Atlantic and Indian Oceans and the China Sea and Sea of Japan are given. Average dust-loadings decrease in the following order: North Atlantic (northeast trades, ∼ 7.7 μg/m 3 of air) > northern Indian Ocean (∼ 1.2 μg/m 3 of air) > South Atlantic (southeast trades, ∼ 0.78 μg/m 3 of air) = southern Indian Ocean (∼ 0.68 μg/m 3 of air) > China Sea (∼ 0.21 μg/m 3 of air). There are differences in the clay mineralogies of dusts transported in similar latitudes in the North Atlantic and northern Indian Oceans. Dusts in the Atlantic northeast trades are dominated by kaolinite from the soils of equatorial Africa; dusts in the northeast monsoons of the northern Indian Ocean have a source in the arid regions of the Rajasthan desert where illite is the principal clay mineral. In the regions investigated quartz occurs in larger amounts in the dusts of the Northern Hemisphere (∼ 7% quartz) than those of the Southern Hemisphere (∼ 3% quartz) over both the Atlantic and Indian Oceans. From the results given in the present paper and those reported in the literature a map is presented illustrating the order of magnitude of lower atmospheric dust-loadings in part of the world ocean.

A preliminary study of organo-mineral complexes in a glassy volcanic ash soil containing imogolite and allophane as principal clay minerals

A preliminary study of organo-mineral complexes in a glassy volcanic ash soil containing imogolite and allophane as principal clay minerals