Compositional Variations in Smectites: Part I. Alteration of Intermediate Volcanic Rocks. A Case Study from Milos Island, Greece

Christidis, George E.; Dunham, A. C.

doi:10.1180/claymin.1993.028.2.07

Cited by 74 publications

(71 citation statements)

References 38 publications

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“…Bruce (1984) and Eslinger et al (1979) reported that the smectites of Mississippi River shales consist of beidellite and montmorillonite, and that the smectites within Cretaceous bentonites before illitization have a tetrahedral charge of 0.6 and an octahedral charge of 0.2. Since natural smectites in the montmorillonite-beidellite series generally possess negative charge for either the tetrahedral and octahedral sheets (Lagaly et al 1976;Nadeau et al 1985b;Malla and Douglas 1987b;Christidis and Dunham 1993), it is possible that a component with tetrahedral charge exists as a precursor smectite and smectite layers in I/S.…”

Section: Discussionmentioning

confidence: 99%

Change in Layer Charge of Smectites and Smectite Layers in Illite/Smectite During Diagenetic Alteration

Satō

1996

Clays and clay miner.

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Abstract--The changes in amount and location of layer charge during diagenetic alteration have been investigated for smectites and smectite layers of illite/smectite interstratified minerals (US) by X-ray powder diffraction analysis with various expansion behavior tests: 1) ethylene glycol (EG) solvation (XRD); 2) K-saturation and EG solvation; 3) Li-saturation, heating at 250 ~ and glycerol or EG solvation (Greene-Kelly test); and 4) alkylammonium saturation. In the course of low-temperature diagenesis but before the onset of illitization, mean layer charge of smectites continuously increases from approximately 0.56 to 0.73 per O20(OH)4 with increasing depth, and tetrahedral charge also increases continuously from approximately 0.21 to 0.38 per O20(OH)4 (beidellitization). The continuous increase in tetrahedral charge without change in peak intensity and shape suggests that the solid-state A1 for Si substitution mechanism appears to predominate within beidellitization. After illitization, the content of the beidellitic layers continuously decreases, while the mean layer charge of expandable layers and the content of illite layers in I/S increase. This suggests that the conversion of a beidellitic layer to an illitic layer preferably occurs during early illitization. Thus, before illitization, beidellite-like layers are formed from precursor smectite, and during the early stage of illitization, the high charged beidellitic layers are probably consumed to form illite layers.

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Section: Discussionmentioning

confidence: 99%

Change in Layer Charge of Smectites and Smectite Layers in Illite/Smectite During Diagenetic Alteration

Satō

1996

Clays and clay miner.

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“…The conditions used for smectite analysis were described by Christidis and Dunham (1993). The same conditions were used for zeolites except for the use of a defocused beam (20 ixm vs. 5 pan used for smectites) and a shorter count time (25 s vs. 100 s used for smectites).…”

Section: Methodsmentioning

confidence: 99%

Formation and Growth of Smectites In Bentonites: A Case Study From Kimolos Island, Aegean, Greece

Christidis

2001

Clays and clay miner.

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Abstract--The low-temperature alteration of a rhyolitic rock from Kimolos Island, Aegean, Greece, yielded an alteration profile characterized by gradual transition from fresh glass to bentonite containing homogeneous Chambers-type montmorillonite and then to a mordenite-bearing bentonite. Both mordenite and smectite were formed from poorly crystalline precursors, which probably had compositions comparable to that of the crystalline end-product. However, their composition may have been modified to some degree after reaction with the fluid phase. Particle length and width measurements of smectite crystals yielded lognormal profiles, which suggest supply-controlled crystal growth in an open system or random ripening in a closed system. The former mechanism is in accordance with the observed sustained supply of Mg and Fe by the fluid phase throughout the alteration profile and is believed to be the dominant formation mechanism of smectites in bentonites in general. In the mordenite-bearing zone, random ripening is expected in domains with low permeability, in which the system was essentially closed, favoring the formation of mordenite. The level of supersaturation with respect to smectite was probably lower in the mordenite-bearing zone. Smectite probably affected pore-fluid chemistry either through ion exchange or via dissolution of initially formed K-bearing smectite. The latter process raised the K+/(Na + + Ca 2+) activity ratio of the pore-fluid favoring K-bearing mordenite.

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“…Also, the speciation of clays, in particular that of montmorillonite, has implications for the cloud and ice nucleation properties of mineral dust and the estimate of iron fractional solubility (Hoose et al, 2008;Journet et al, 2008). Ultimately, these facts depend on the compositional heterogeneity in Al-rich smectite in the natural soils and sediments (Christidis and Dunham 1993;Christidis, 2006), due to various processes, including weathering and/or hydrothermal alteration of basic rocks (Köster et al, 1999) but also due to reduction reactions of structural Fe by microorganisms (Pentrakova et al, 2013). This makes the quantification extremely dependent on the environmental conditions.…”

Section: Final Remarks Conclusion and Perspectivesmentioning

confidence: 99%

Mapping the physico-chemical properties of mineral dust in western Africa: mineralogical composition

et al. 2014

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Abstract. In the last few years, several ground-based and airborne field campaigns have allowed the exploration of the properties and impacts of mineral dust in western Africa, one of the major emission and transport areas worldwide. In this paper, we explore the synthesis of these observations to provide a large-scale quantitative view of the mineralogical composition and its variability according to source region and time after transport.This work reveals that mineral dust in western Africa is a mixture of clays, quartz, iron and titanium oxides, representing at least 92 % of the dust mass. Calcite ranged between 0.3 and 8.4 % of the dust mass, depending on the origin. Our data do not show a systematic dependence of the dust mineralogical composition on origin; this is to be the case as, in most of the instances, the data represent the composition of the atmospheric burden after 1-2 days after emission, when air masses mix and give rise to a more uniform dust load. This has implications for the representation of the mineral dust composition in regional and global circulation models and in satellite retrievals.Iron oxides account for 58 ± 7 % of the mass of elemental Fe and for between 2 and 5 % of the dust mass. Most of them are composed of goethite, representing between 52 and 78 % of the iron oxide mass. We estimate that titanium oxides account for 1-2 % of the dust mass, depending on whether the dust is of Saharan or Sahelian origin.The mineralogical composition is a critical parameter for estimating the radiative and biogeochemical impact of mineral dust. The results regarding dust composition have been used to estimate the optical properties as well as the iron fractional solubility of Saharan and Sahelian dust.Data presented in this paper are provided in numerical form upon email request while they are being turned into a public database, the Dust-Mapped Archived Properties (DUST-MAP), which is an open repository for compositional data from other source regions in Africa and worldwide.

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Compositional Variations in Smectites: Part I. Alteration of Intermediate Volcanic Rocks. A Case Study from Milos Island, Greece

Cited by 74 publications

References 38 publications

Change in Layer Charge of Smectites and Smectite Layers in Illite/Smectite During Diagenetic Alteration

Change in Layer Charge of Smectites and Smectite Layers in Illite/Smectite During Diagenetic Alteration

Formation and Growth of Smectites In Bentonites: A Case Study From Kimolos Island, Aegean, Greece

Mapping the physico-chemical properties of mineral dust in western Africa: mineralogical composition

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