Vermiculitisation expérimentale d'une chlorite

Abstract--X-ray diffraction, FTIR, and chemical analyses were performed on clay fractions (1-2/~m, <0.1 pm), separated by means of size fractionations and high-gradient magnetic separation techniques, from a Cryorthod developed in a chlorite-mica schist saprolite. Weathering of large phyllosilicates preexisting in the saprolite involves physical fragmentation and mineralogical transformations. Chloritic minerals in the coarse fractions were the most affected by physical breakdown, while micas were generally preserved. As a consequence, a concentration of mica layers occurred in the coarse clay fraction, while chloritic residues accumulated in the fine clays. These residues exhibited the typical XRD pattern of hydroxy-interlayered intergrade minerals, but the interlayered contaminants were found to be mainly hydroxy-Mg cations. Further mineralogical transformations of the intergrade minerals involved the progressive removal of the hydroxide interlayered sheet and dissolution of chloritie layers. Illite/smectite mixed-layers were formed in the surface horizon of the soil profile. These processes were associated with a strong decrease in Fe and Mg contents in the clay fractions.

Section: Ftir Spectroscopymentioning

confidence: 96%

Characterization of Hydroxy-Interlayered Vermiculite and Illite/Smectite Interstratified Minerals from the Weathering of Chlorite in a Cryorthod

Righi

1993

“…Furthermore, the insensibility of the bands near 3400 and 3540 cm -1 corresponding to OH in the hydroxide interlayer toward oxidation and reduction seems to preclude Fe(II) in the hydroxide sheet. Chemical analysis shows that Fe(II) is unlikely in the hydroxide sheet because the amounts of AI, Fe, and Mg extracted after oxidation are much smaller than those extracted by Makumbi and Herbillon (1972) and Ross (1975) from chlorites which they considered to contain Fe(II) in the hydroxide sheet. The DTA-EGA data, showing no correlation between the oxidation processes and the main dehydroxylation peak of the hydroxide interlayer at 610~ also support the assignment of original Fe(II) to the 2:1 layer.…”

Section: Location Of Octahedral Cationsmentioning

confidence: 99%

“…The two processes may be separated by thermal oxidation of the iron succeeded by acid dissolution of the hydroxide interlayer (Ross and Kodama, 1974;Goodman and Bain, 1979). During dry thermal oxidation, the layer charge remains constant by the release of one hydrogen atom per oxidized Fe(II), as suggested in the oxidation of biotite (Vedder and Wilkins, 1969;Farmer et al, 1971;Veith and Jackson, 1974;Hogg and Meads, 1975;Tripathi et al, 1978;Bagin et al, 1980), chlorite (Makumbi and Herbillon, 1972;Goodman and Bain, 1979), and smectite Heller-Kallai, 1976a, 1976b). For chlorite, the mechanism of this hydrogen release is obscure, as is the reversibility of the oxidation step.…”

Section: Introductionmentioning

confidence: 99%

“…The alteration of chlorite to vermiculite is considered to take place via an oxidation and subsequent removal of structural iron from the hydroxide interlayer (Makumbi and Herbillon, 1972;Ross, 1975;Ross andKodama, 1974, 1976;Goodman and Bain, 1979). The two processes may be separated by thermal oxidation of the iron succeeded by acid dissolution of the hydroxide interlayer (Ross and Kodama, 1974;Goodman and Bain, 1979).…”

Section: Introductionmentioning

confidence: 99%

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Oxidation and Reduction of Structural Iron in Chlorite at 480°C

Borggaard¹,

Lindgreen²,

Mørup

1982

Abstract--An iron-rich chlorite, ripidolite, was oxidized by air-heating at 480~ i.e., below the dehydroxylation temperature and subsequently reduced in hydrogen at the same temperature. On the basis of chemical, differential thermal, infrared, MSssbauer, and X-ray powder diffraction analyses, Fe(II) seems to be present only in the 2:1 layer of the original chlorite in a type of site similar to that of Fe(II) in biotite, with OH in cis-positions. These data also suggest that octahedral A1 and Fe(III) are located in the hydroxide sheet of the original chlorite. The structural changes of the mineral due to the oxidation and the subsequent reduction appear limited to minor structural rearrangements and, perhaps, to the introduction of OH in

“…The removal of iron from the chlorite hydroxide sheet is an essential part of the process, and a high iron concentration in the hydroxide sheet appears to be a necessary prerequisite for chlorite vermiculitization. The iron can be oxidized (Makumbi and Herbillon, 1972;Ross, 1975) or unoxidized (Proust et al, 1986) by the vermiculitization process, and sedimentary goethite is sometimes reported as a reaction product (Anand and Gilkes, 1984).…”

Section: Introductionmentioning

confidence: 99%

Chlorite Vermiculitization and Pyroxene Etching in an Aeolian Periglacial Sand Dune, Allen County, Indiana

Argast

1991

Abstract--Weathering has etched and deeply-dentieulated the constituent orthopyroxenes, and chlorite has been transformed to vermiculite in the upper 3 m of an aeolian, periglacial sand dune formed in northeastern Indiana about 13,000 b.p. Pyroxene weathering begins with the development of cleavageparallel etch pits on {010} and ( 100 } surfaces. These pits coalesce and eventually crop out on basal surfaces as denticulations. The mean denticulation size increases logarithmically toward the surface, and the denticulation size of the orthopyroxenes is a quantifiable feature of the weathering process. Ferruginous pendants, microboxworks of iron oxides, and other indications of iron redeposition within the orthopyroxene microenvironments were not observed.Chlorite in the dune has been weathered to vermiculite. The parent chlorite is a high-Fe variety, and the transformation to vermiculate does not involve the development of a chlorite/vermiculite intermediary phase. Fe 2 § is oxidized as part of the transformation process and this iron is retained in the sediment as discrete goethite and as crystalline and noncrystalline coatings on the dune grains. The vermiculite from depths shallower than 64 cm is only partly expandable and is completely collapsed by K-saturation or heat treatment. This is a hydroxy-A1 vermiculite and its formation is typical of intense weathering under the acid conditions prevalent at the dune surface.