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

Abstract

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.

Weathering of Chlorite to a Low-Charge Expandable Mineral in a Spodosol on the Apennine Mountains, Italy

“…This different sensitivity might result from different compositions; for example, Righi et al (1993) found that Mg-interlayers were scarcely sensitive to Na-citrate, while Al-interlayers are known to be removed in this way.…”

“…Recent work on both Spodosols and environmentally associated Dystrochrepts (Righi and Meunier 1991;Righi et al 1993) has again reported the presence of smectite (identified by EG solvation) components in surface horizons, and of HIM in the B horizons. The authors have, in one case, traced possible origins to either chlorite or mica (Righi et al 1993), while in the other case (Righi and Meunier 1991) they have attributed the genesis of the low-charge expandable mineral to weathering of mica, although chlorite was present in the parent material.…”

“…The authors have, in one case, traced possible origins to either chlorite or mica (Righi et al 1993), while in the other case (Righi and Meunier 1991) they have attributed the genesis of the low-charge expandable mineral to weathering of mica, although chlorite was present in the parent material. This last interpretation was based again on the concept of chlorite de- Ross (1980) pointed out how this is in apparent disagreement with thermodynamic equilibrium calculations, and endorsed the view that this contrast is due to incomplete evolution, and then nonequilibrium, of soils that, in most cases, are geologically young and develop in rather cool climates.…”

Argilominerais em solos de manguezais da costa brasileira

“…Isso demonstra que o grau de intercalação é suficientemente forte para não ser alterado por este tratamento, especificamente. É provável que um tratamento por mais horas seja efetivo nesse sentido, ou que as lâminas não sejam compostas por hidróxidos de Al, e sim de Mg (Mg(OH) 2 ), o que pode tornar a extração pelo citrato menos eficiente (RIGGHI et al, 1993). Figura 41 -Exemplos de difratogramas de argila fina (<0,2 μm) submetida ao tratamento com citrato de sódio, a 100ºC.…”

“…Figura 41 -Exemplos de difratogramas de argila fina (<0,2 μm) submetida ao tratamento com citrato de sódio, a 100ºC. A ausência do colapso do pico a 1,2-1,3 nm é indica duas possibilidades: ausência de polímeros de hidróxido de Al, com a presença de lâminas de hidróxiods de Mg (Rigghi et al, 1993) na entrecamada nas esmectitas; ou ineficiência do tratamento para eliminar esse material (tempo insuficiente) de micas trioctaédricas, comuns nos difratogramas em pó não orientado da argila total.…”