Laboratory Alteration of Trioctahedral Micas

Abstract--Highly tectonized contact between serpentinite and younger pegmatite in the magnesite mine of Wiry contains various layer silicates. Vermiculite, chlorite, smectite, and interstratified mica-vermiculite were recognized by means of routine XRD examination. Two three component interstratifications of mica-vermiculite-chlorite and chlorite-swelling cblorite-smectite were identified by a combined procedure of deconvolution of the XRD patterns and simulation of XRD tracings. A mineral with large diffraction maxima, displaying "chlorite intergrade" characteristics, appeared to be a mixture of chlorite, mixed layer chlorite-smectite, and vermiculite. Polytypes of phyllosilicates were determined by the X-ray transmission method. Due to the heritage of parent mineral polytype structure by transitional products of alteration, two distinct sequences of layer silicates were observed: one formed from trioctahedral mica (vermiculite, mixed layer mica-vermiculite); and one evolved from chlorite (e.g., mixed layer chlorite-swelling chloritesmectite). A tentative scheme of the primary contact zone structure, not obscured by subsequent brittle tectonics either by transformation of layer silicates, is proposed.

“…Similar sequences of layer silicates were obtained during experimental alteration studies (e.g., Rich, 1968;Hoda and Hood, 1972;Ross andKodama, 1974, 1976).…”

Section: Introductionsupporting

confidence: 69%

Layer Silicates from Serpentinite-Pegmatite Contact (Wiry, Lower Silesia, Poland)

Jelitto¹

1993

“…The hydroxyl ions ofdioctahedral smectite orient slightly toward the empty octahedral site, and the repulsive force of montmorillonite and beideUite is relatively weaker. The influence of hydroxyl ions on the fixation of interlayer cations in the silicate network has been reported for micas (Bassett, 1960;Newman, 1969;Hoda and Hood, 1972). The negative charge distribution of the present saponite is -0.13/O~o(OH)2 in the octahedral sheet and -0.23/ O~0(OH)2 in the tetrahedral sheets.…”

Section: Clays and Clay Mineralssupporting

confidence: 52%

Dehydration and Rehydration of Saponite and Vermiculite

Kawano

Tomita

1991

Abstract--The rehydration properties and behavior of interlayer cations of Ca-, Mg-, Na-, and K-saturated homoionic saponite and vermiculite heated at various temperatures were examined and their rehydration mechanisms elucidated. The most notable features of saponite were (1) except for the Mgsaturated specimen, all saponite samples rehydrated until the crystal structure was destroyed by heating; (2) the rehydration rate in air after heating decreased in the order: K + > Na § > Ca 2+ > Mg2+; (3) the interlayer cations apparently migrated into hexagonal holes of the Sit4 network on thermal dehydration; and (4) the b-parameter expanded on thermal dehydration. The rehydration properties and behavior of interlayer cations of vermiculite were: (1) except for the K-saturated specimen, all vermiculite samples rehydrated until the crystal structure was destroyed by heating; (2) the rehydration rate in air after heating decreased in the order: Mg 2+ > Ca ~+ > Na + > K+; (3) the interlayer cations apparently did not migrate into the hexagonal holes, but remained at the center of the interlayer space, even after thermal dehydration; and (4) except for the K-saturated specimen, the b-parameters of the samples contracted on thermal dehydration. The different rehydration properties of saponite and vermiculite were apparently due to the behavior of the interlayer cations during thermal dehydration. For rehydration to occur, the interlayer cations of saponite had to migrate out of the hexagonal holes. Consequently, saponite saturated with a large cation rehydrated rapidly, whereas saponite saturated with a small cation rehydrated slowly. On the other hand, the interlayer cations of vermiculite remained in the interlayer space; therefore, the rehydration properties of vermiculite were strongly affected by the hydration energies of the interlayer cations. Furthermore, electron diffraction patterns suggested that the saponite and vermiculite consisted of random stacking and ordered stacking of adjacent 2:1 layers, respectively. The nature of the stacking of the minerals seemed to be the most important factor controlling the behavior of interlayer cations in the thermal dehydration process.

“…Rausell- Colom et al (1965) and Hoda and Hood (1972) have stated that interstratification would be expected in dilute salt solution and the slow replacement of K, as natural weathering. From recent TEM study, it has been illustrated that in natural weathering single vermiculite layer occurred sporadically throughout the mica grain, or mica-vermiculite pairs developed (Banfield and Eggleton 1988).…”

Section: The Effect Of the Release Rate O F K On The Development O F mentioning

confidence: 99%

Dissolution Process of Phlogopite in Acid Solutions

Kuwahara

Aoki

1995

Abstract--The alteration experiments of phlogopite with 0.01 N HC1 solution containing 0.1 M NaC1 at 50*, 80* and 120"C have been carried out to aid in the understanding of the dissolution process of mica and the formation of secondary phases such as vermiculite and interstratified mica/vermiculite. Twenty milligrams of phlogopite samples were suspended in 20 ml or 100 ml of leaching solution.In these experiments, the dissolution ofphlogopite occurred incongruently, where the preferential release of K occurred in almost all stages of the alteration reaction. In the 100 ml experiments, the priority in dissolution in the initial stage was in the order; K > Fe > Mg, Al > Si. This supports that phlogopite leaching is controlled by the mineral structure. At 80* and 50"C in the 20 ml experiments, the release of all elements except for K was nearly congruent. At 120"(2 in the 20 ml experiments, the dissolution was outwardly incongruent, which Fe decreased remarkably after six days and A1 was released most slowly compared with all other elements in phlogopite. This is probably due to the precipitation of secondary phases such as aluminum and iron oxides and/or hydroxides.Vermiculite and Rl-type interstratified mica/vermiculite, containing 70 -50% mica, were formed in the alteration process of phlogopite. The following two processes were confirmed for the formation of interstratified structure: Interstratified structure was formed (1) directly from phlogopite or (2) from vermiculite which was produced earlier from phlogopite by regaining of K from the ambient solution. It may depend on the release rate of K from phlogopite whether mica-vermiculite layer sequences develop or vermiculite-vermiculite sequences do.