Talc Layers Research Articles

Modeling of interaction properties of surfaces of phyllosilicates: A theoretical forecast of adsorption isotherms of noble gases at the talc surface

The electrostatic potential and the intensity of the electric field above the isolated layer of the phyllosilicate mineral talc (layer group symmetry C2/m) were computed using the semiempirical INDO/2 method. The electrostatic potential Vc and the intensity of electric field (OVERBAR)Ec, above the surface of semi-infinite crystal were obtained as the sum of the contributions of the infinite number of individual layers. The interaction energy Uint between a noble gas atom and the talc crystal was computed as (a) a pure Lennard-Jones energy ULJ and (b) the sum of ULJ and interaction energy with induced dipole moment: Uind = α|(OVERBAR)E|2, where α is the dipole polarizability of the noble gas atom. The one-particle configurational integral was calculated within the classical mechanics limit. Both the free and adsorbed gas phases were assumed to be ideal. The obtained results demonstrate that in the case of uncharged and nonpolar adsorbate and an uncharged surface the electrostatic part of the interaction energy should be included in the total interaction energy. © 1996 John Wiley & Sons, Inc.

Oxidation character of chlorite from Byrapur chromite deposit, India — A57Fe Mössbauer evaluation

Chlorite occurring in tremolite-chlorite schist rock of Byrapur chromite deposit of southern India has been investigated by57Fe Mössbauer spectroscopy along with XRD, IR and EPMA analyses. From XRD and EPMA results the chlorite is identified as clinochlore. The fit of Mössbauer spectrum (at room temperature) shows five symmetric doublets for iron. Based on hyperfine parameters three doublets are assigned to Fe2+ attrans andcis positions of talc layers, and Fe2+ at brucite layer. The remaining two doublets are attributed to Fe3+ attrans position and Fe3+ at tetrahedral site. The Mössbauer result suggests that the Fe3+ in octahedral sites of this chlorite was caused by oxidation after chloritization. The chlorite of Byrapur area was less oxidized compared to the chlorite of Sukinda chromite deposit of eastern India.

A theoretical study on the interaction between talc layers.

The interaction between the talc layers is studied for a model system of two tetrahedral sheets. The upper sheet is a unit cell of tetrahedral sheet, [Si 4 O 10 ] 4− and the lower sheet an infinite hexagonal network of [SiO 4] 4− . Using the electrostatic and Lennard-Jones equations, the energy for the interlayer interaction is calculated under the periodic boundary conditions. It is concluded that the interaction between the above two silicate sheets is attractive

Fragments et granules contenant de la matière organique dans le Proterozoïque supérieur du Congo

We show the occurence of anthracite and immature organic matter bearing talc clasts or granules within the regressive sive sequence of the Schisto-calcaire cycle (West Gongolian Supergroup) which is interpreted as a carbonate ramp. The sedimentary succession of the Makanfou river corresponds to a reflective beach. The supratidal withish dolomite (SCIIIc) bears immature organic matter bearing talc clasts and layers. The SCIIIb facies corresponds to the intertidal domain marked out by a dark stratiform dolomitic stromatolite composition. It also corresponds to the infratidal domain. A slice of dark dolomite bears immature organic matter bearing algal lamines, angular, ribbon like shaped or ovoid clasts, and mature organic matter bearing brownish granules matter which are more often radial with micritic cones. The particular preservation of the organic matter is effectued in a poor oxygen water of lagoon. Clasts bearing anthracite and mature organic matter deposited away dark limestones at deeper water. These black talc clasts likely correspond to slices of the intertidal stromatolites. Moreover, immature organic matter bearing granules with radial brownish cones occur within a pebble of the fluvio-estuarine SCIV facies. The occurrence of immature and mature organic matter in such ancient sediments shall be underlined. The sedimentary evolution of the algal lamines started by a mechanical disruption followed by a dynamic erosion of the clasts. Then, the organic matter undergone, a brown coloration by coloration by centrifuge and/or centripete migration which also developped as radial penetrative cone. Eventually, a centripete radial micritisation may affect the brown clasts. The brown coloration modified mature organic matter rather than the micritisation which destroyed the organic matter. The organic mater bearing radial granules, do not correspond to oolites or micro-organisms. They are biodetrital mater derived from algal lamines.

Geochemistry and mineralogy of laterites in the Sula Mountains greenstone belt, Lake Sonfon gold district, Sierra Leone

Geochemical and mineralogical investigations have been carried out on laterite profiles developed in the Lake Sonfon Au district of northern Sierra Leone. The area is underlain by Archean metavolcanics and constitutes part of the Sula Mountains greenstone belt, which is mineralized in Au. Extensive lateritization has affected the rocks of this region, resulting in a profile which from bottom to top consists typically of a decomposed bedrock zone, a pisolitic laterite layer and a duricrust layer. Both the pisolitic and duricrust layers of the laterite are sometimes punctuated by lenses of ironstones containing high amounts of Cu, Zn, Ni, Co and Ce. Gold occurs as small grains within the heavy mineral fraction recovered from the decomposed rock zones and pisolitic layers of the profiles and also in gravels of streams draining the area. The mineralogy of the duricrust and pisolitic layers is dominated by goethite, gibbsite and quartz, with minor amounts (<5% by volume) of ilmenite, magnetite, haematite, rutile and kaolinite. The kaolinite content increases towards the decomposed rock zone, where talc, vermiculite and other layer lattice silicates become abundant. The heavy-mineral fraction of stream sediments is composed essentially of ilmenite, magnetite, haematite, and traces of rutile, zircon, tourmaline and Au. The Au grains are often characterized by a 10–200-μm-wide rim having a much lower content of Ag (0.3 wt.% or lower) than the grain interior (about 5 wt.% on average). Dissolution effects are also observed on the grain surfaces. It is considered that Au derived from the amphibolite parent rock is dissolved, transported, and redeposited during laterization. The duricrust cover of the laterite profiles is characterized by high contents of Fe2O3 (ca. 60 wt.%) and Al2O3 (ca. 32wt.%) and low content of SiO2 (ca. 9 wt.%). In comparison, the pisolitic layer is higher in SiO2 (ca. 18 wt.%) as well as a slightly higher in Al2O3 (ca. 34 wt.%). Lateritic weathering has resulted in the removal of CaO, Na2O, MgO and SiO2, with relative enrichment of Fe2O3 and Al2O3. The geochemical distribution of the trace elements in the laterite profiles can be related to the occurrence of the auriferous mineralization. The significance of these observations is discussed in relation to the origin of the lateritic Au and the role of the associated trace elements as indicators of the mineralization.

Low-Temperature Oolitic Talc in Upper Proterozoic Rocks, Congo

ABSTRACT A black granule layer in the Precambrian West-Congolian Mountain Range has been studied. Situated in a calcareous and dolomitic unit of the Schisto-Calcaire group of the West-Congolian System, this layer, called the Pseudo-Oolithe de Kisantu, is found in all this part of southwest Africa. It is composed of millimeter-sized spheroids or ovoids of pure talc in a siliceous matrix, with minor amounts of calcite, dolomite and sulfate. These oolites have a homogeneous chemical composition and do not contain organic matter. Their oxygen isotopic composition (+18 versus SMOW) is within the range of low-temperature clay minerals and outside the composition range of hydrothermal talcs. After comparison with other authigenic Mg-clays found n salt-bearing or evaporitic environments, the proposed origin for this oolitic talc layer is a two-step process: 1) direct precipitation of stevensite or sepiolite at low temperature in shallow marine, low salinity waters; 2) transformation of the stevensite (or sepiolite) into talc during diagenesis.

Magnetic properties of sheet silicates; 2:1:1 layer minerals

Magnetization, susceptibility and M6ssbauer spectra are reported for representative chlorite samples with differing iron content. The anisotropy of the susceptibility and magnetization of a clinochlore crystal is explained using the trigonal effective crystal-field model developed earlier for 1:1 and 2:1 layer silicates, with a splitting of the Tzg triplet of 1,120 K. Predominant exchange interactions in the iron-rich samples are ferromagnetic with J= 1.2 K, as for other trioctahedral ferrous minerals. A peak in the sus- ceptibility of thuringite occurs at Tm = 5.5 K, and magnetic hyperfine splitting appears at lower temperatures in the M6ssbauer spectrum. However neutron diffraction reveals no long-range magnetic order in thuringite (or biotite, which behaves similarly). The only magnetic contribution to the diffraction pattern at 1.6 K is increased small angle scattering (q<0.4~ 1). A factor favouring this random ferromagnetic ground state over the planar antiferromag- netic state of greenalite and minnesotaite is the presence of pairs of ferric ions on adjacent sites, in conjunction with magnetic vacancies in the octahedral sheets. Monte Carlo simulations of the magnetic ground state of the sheets illus- trate how long range ferromagnetic order may be destroyed by vortices forming around the Fe 3 +--Fe 3 + pairs. tral in chlorites. Substitution of trivalent ions for Mg in the brucite layers is compensated by replacement of Si by A1 in the tetrahedral sheets of the talc layers (Bailey 1980). The general formula for a trioctahedral chlorite is

Reactions between natural serpentinite and quartz under hydrothermal conditions. (1) On synthesis of diopside fiber under hydrothermal condition.

Hydrothermal experiments in the system MgO–SiO2–H2O were carried out with the use of natural serpentinite as starting materials without crushing. The serpentinite specimen was prepared as a prismatic form of about 4 mm × 4 mm × 20 mm in size. A serpentinite prism was put into a silver capsule together with fine quartz powder and distilled water. Both sides of the capsule were sealed by welding. All experimental runs were made at 1,000 bars in pressure and at 360°C, 450°C, 495°C and 540°C in temperature. The duration times for maintaining constant temperature were from 16 to 1,000 hours. At temperatures above 450°C, in most experiments many white fibrous diopside crystals grew on surface of the serpentinite specimen. A talc layer was formed at the marginal part of serpentinite specimen, its thickness varied from 0 to 50 μm through all experiments. At temperatures below 360°C, serpentine minerals were preserved in the inner part of the specimen, but at temperatures above 450°C, olivine crystals were formed. These reaction processes were discussed.

Reactions between natural serpentinite and quartz under hydrothermal conditions. (2) On migration of SiO2 and calcium through serpentinite under hydrothermal condition.

Hydrothermal reactions between natural serpentinite and quartz powder was reported in our previous paper. A thin talc layer was formed over the whole surface of serpentinite due to the reaction with quartz and H2O. In most treatment at temperatures above 450°C, many fibrous diopside crystals grew on the surface of the serpentinite prism toward the outside. This paper gives some considerations on the migration mechanism of chemical elements responsible for these hydrothermal reactions.The relation between average thickness and experimental conditions shows that the chemical components were transported by mean of diffusion process, and an activation energy for diffusion is 21.5 kcal/mol. Diffusion coefficient in the 5 μm thick talc layer is 10−6.5 cm2/sec, and that in the 10 μm thick layer is 10−5.5 cm2/sec.The migration process of a chemical component is closely related to its solubility in hydrothermal solutions. The solubilities of MgO and CaO are related to pH of the solution. The pH values of the solution through which CaO will migrate but MgO will not, should be in a restricted condition.During the formation of diopside crystals, CaO must have been supplied from inside of the serpentinite by H2O solution. The rate of movement of the solution was calculated by diffusion process. The diffusion coefficient of solution in serpentinite was estimated as 4.5×10−4 cm2/sec. It may be concluded that the solution moved very easily through solid serpentinite.

Hydrothermal Reactivity of Saponite

AbstractSaponite crystallizes from amorphous gel having an ideal saponite composition within 7 days at all experimental temperatures between 300° and 550°C at 1 kbar pressure. Reactions subsequent to this initial crystallization vary in type and degree, depending on the temperature of reaction and the type of interlayer cation. Above 450°C, the intitially crystallized K-saponite dissolves, and talc and phlogopite nucleate and grow as discrete phases. At 450°C the initial K-saponite reacts to form talc and phlogopite layers, but the reaction proceeds via intracrystalline layer transformations rather than via dissolution and precipitation, producing a mixture of fully ordered, interstratified talc/saponite and fully ordered saponite/phlogopite. The K-saponite shows subtle signs of reaction at 400°C after 200 days: this temperature is at least 150°C lower than experimental reaction temperatures previously reported for saponites. No reactions beyond the initial crystallization of saponite were observed below 400°C. K-saponite reacts more rapidly than either Na-saponite or Ca-saponite above 400°C, and the Na-saponite and Ca-saponite produce no mica layers during their transformation to mixed-layer clays. Interstratified talc/saponite formed in the Na-saponite system, and the Ca-saponite system produced both talc/saponite and chlorite/saponite.

Morphology and alteration of asbestiform grunerite and anthophyllite

AbstractSections perpendicular to [001] of ion-thinned specimens of amosite (fibrous grunerite) from Penge, Transvaal and anthophyllite from Paakila, Finland and Söndeled, Norway, have been examined by high-resolution transmission electron microscopy. Observations on the nature of grain boundaries and alteration are compared with those of other workers on other fibrous amphiboles. Fibrous crystals grow with their fibre (c) axes approximately parallel to one another but they have considerable rotational disorder about that axis. Grain boundaries are generally irregular in shape and only follow low-index planes for short sections. In all specimens the amphibole has undergone some alteration to sheet silicates along grain boundaries, fractures, cleavages, and multiple-chain lamellae. Anthophyllite alteration products are talc, serpentine and chlorite, and amosite alteration products approximate to iron analogues of talc and serpentine. Talc layers are generally planar and their orientation is strongly controlled by the amphibole structure, whereas serpentine and chlorite layers often curve and their orientations are less frequently related to that of the amphibole. Comparison of specimens which appear finely fibrous in hand specimen with those which appear coarser, acicular or massive suggests that the nature of fibres produced by crushing is mainly controlled by the grain boundaries in the former type, but other factors such as fractures, cleavages, and defects are more important for the latter types.

Serpentine Minerals: Intergrowths and New Combination Structures

The serpentine minerals chrysotile, lizardite, and antigorite have been found intimately intergrown with each other and with talc, chlorite, and amphibole in incompletely reacted chain silicates. High-resolution transmission electron microscopy has revealed new variations in serpentine planar and roll structures, as well as regions of mixed-layer silicate consisting of serpentine and talc layers.

Isolation of animal viruses from farm livestock waste, soil and water.

Ten porcine enteroviruses, 2 porcine adenoviruses and 1 coronavirus were isolated directly from 32 samples of slurry collected from a pig fattening house. Concentration of the same samples by adsorption with the polyelectrolyte PE-60 yielded 24 porcine enteroviruses and 3 porcine adenoviruses. A porcine enterovirus was isolated, following PE-60 concentration, from 1 to 6 slurry samples from a sow farrowing house. No virus was isolated from 12 samples of slurry from dairy cows nor from 6 slurry samples from a calf-rearing unit. A porcine enterovirus was isolated from soil samples, after concentration with PE-60, collected 1, 2 and 8 days after pig slurry was spread on hay stubble. Two porcine enteroviruses were isolated by membrane filtration from 26 samples of surface run-off from land on which pig slurry was routinely spread, and 2 bovine enteroviruses were isolated from cattle feedlot run-off after adsorption to layers of talc and celite followed by hydroextraction. A porcine enterovirus was also isolated from 1 of 33 samples of surface water collected on farms on which pig slurry was routinely spread on the land, but no virus was isolated from 36 samples of ground water from the same farms. The surface water and ground water samples were concentrated by talc-celite adsorption and hydroextraction.

Orthopyroxene to talc transformation

Mineralogical transformations that occur during the weathering of rocks are complex processes involving both physical and chemical changes. Although it may be difficult to relate the primary minerals to the secondary phases of the weathering process, there is evidence that certain transformations occur topotaxially. The clinopyroxene, hedenbergite, alters to montronite, an iron-rich montmorillonite mineral, topotaxially; the transformation has been modelled by a crystallographic shear of 1/2[101] on (100) of the pyroxene. This shear mechanism converts the chain silicate into a sheet structure. A similar process may be postulated for several other pyroxene alterations. The commonly observed orthopyroxene to talc transformation has been studied in detail using electron microscopy, electron microprobe, optical microscopy and x-ray diffraction.The process has been studied in an interaction zone that develops between unaltered orthopyroxene and talc layers formed along grain boundaries and within cracks. The growth of the interaction zone occurs by the migration of the interface into the unaltered orthopyroxene-Fig. 1.

Infrared study of 10A type garnierite on the heating.

The 10 A type garnierite from Nakey, New Caledonia was exmained by means of thermal analysis and continuous high-temperature X-ray diffraction technique, and was heated at various temperature up to 1000°C and after each treatment the specimens were cooled and also exmained by X-ray powder diffraction and infrared analysis. The first basal reflection from this 10 A type garnierite is a broad reflection, and its peak profile is asymmetric with a spreading towards smaller angles of 2θ. The basal spacing exhibits little change when the specimens soaked in water or in ethylene glycol. The specimen shows the absorption bands at 3685cm-1, 3643cm-1 and 3625cm-1 in the OH region. The bands at 3690cm-1, 3670cm-1, 3645cm-1 and 3625cm-1 become clear in the temperature range from 250°C to 500°C. The band at 3690cm-1 becomes unrecognizable and the very sharp bands at 3675cm-1, 3660cm-1, 3645cm-1 and 3625cm-1 are recognized in the spectra of the specimens heated to 750°C and 800°C. These infared absorption bands of this specimen which was heated between 750°C and 800°C, are in good agreement with the data of synthetic and natural nickel rich talc, except for strong intensity of the band at 3765cm-1. From the changes of these bands on heating, the material is considered to be either a mixture of nickel rich hydrated talc layer and magnesium rich hydrated talc layer or nickel rich hydrated talc layer with a heterogeneous distribution of Ni and Mg in octahedral layer, and contains extremely small amounts of chrysotile as impurity.

Thin-layer chromatography of free and esterified porphyrins on talc

Free porphyrins and porphyrin esters are clearly and rapidly separated according to the number of carboxyl groups on 70 × 70 mm plates with 0.30 mm thick layers of talc prepared from methanol suspensions. Porphyrins were run with 0.5 N HCl-acetone (3:7) and porphyrin esters with glacial acetic acid-pyridine-acetone (1:1:1). Clear separations were achieved in 10–15 min even in the presence of impurities. Of both, porphyrins and porphyrin esters, the R F value increased with the number of carboxyl groups. The methods are suitable for separating higher carboxyls, but less suitable for porphyrins with less than 4 carboxyl groups. As the opposite is the case with previously described techniques, the methods described here constitute a useful supplement to existing methods. A quick and convenient method of preparing plates from silica gel, kieselguhr, alumina and talc from methanol suspensions is also described.

Triclinic Form of Talc

PAULING1 predicted structures for the individual layers of talc, pyrophyllite and the micas, and these structure determinations have since been shown to be broadly correct. Although accurate structures have been determined for several well crystallized micas, this has not been done for talc.

Über orientierte Aufwachsungen von Kristallen auf Talk und Kadmiumjodid

Oriented overgrowths of crystals of organic compounds on cleavage layers of talc and cadmium iodide and of NH4J on talc are described. These oriented overgrowths are remarkable in view of the fact that thevan der Waals forces between the layers of these substrate crystal lattices are only weak. The crystals of NH4J oriented on talc have a square contour in contrast to the triangular crystals of NH4J oriented on mica.