Some Interstratified Clay Minerals from Basic Igneous Rocks
About: This article is published in Clay Minerals.The article was published on 1960-01-01. It has received 8 citations till now. The article focuses on the topics: Aluminosilicate & Clay minerals.
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01 Jan 1975
TL;DR: In this article, it was verified that this irregularity was due to the interstratification of different types of crystalline layers, which is a phenomenon that was first observed on studying clay minerals by X-ray diffraction.
Abstract: Interstratification is a phenomenon that was first observed on studying clay minerals by X-ray diffraction. It was noted that the majority of them had basal reflections (001), which did not form a regular series. It was verified that this irregularity was due to the interstratification of different types of crystalline layers.
184 citations
TL;DR: In this article, a combination of TEM/AEM, EMPA, XRD, and optical microscopy was used to study low-grade metamorphic or hydrothermally altered mafic rocks.
Abstract: Many chloritic minerals in low-grade metamorphic or hydrothermally altered mafic rocks exhibit abnormal optical properties, expand slightly upon glycolation (“expandable chlorite”) and/or have excess AlVI relative to AlIV, as well as significant Ca, K and Na contents. Chloritic minerals with these properties fill vesicles and interstitial void space in low-grade metabasalt from northern Taiwan and have been studied with a combination of TEM/AEM, EMPA, XRD, and optical microscopy. The chloritic minerals include corrensite, which is an ordered 1:1 mixed-layer chlorite/smectite, and “expandable chlorite”, which is shown to be a mixed-layer chlorite/corrensite. Corrensite and some mixed-layer chlorite/corrensite occur as rims of vesicles and other cavities, while later-formed mixed-layer chlorite/corrensite occupies the vesicle cores. The TEM observations show that the mixed-layer chlorite/corrensite has ca. 20%, and the corrensite has ca. 50% expandable smectite-like layers, consistent with XRD observations and with their abnormal optical properties. The AEM analyses show that high Si and Ca contents, high AlVI/AlIV and low FeVI/(Fe+Mg)VI ratios of “chlorites” are correlated with interstratification of corrensite (or smectite-like) layers in chlorite. The AEM analyses obtained from 200–500 A thick packets of nearly pure corrensite or chlorite layers always show that corrensite has low AlIV/SiIV and low FeVI/(Fe+Mg)VI, while chlorite has high AlIV/SiIV and high FeVI/(Fe+Mg)VI. This implies that the trioctahedral smectite-like component of corrensite has significantly lower AlIV/SiIV and FeVI/(Fe+Mg)VI. The ratios of FeVI/(Fe+Mg)VI and AlIV/SiIV thus decrease in the order chlorite, corrensite, smectite. The proportions of corrensite (or smectite-like) layers relative to chlorite layers in low-grade rocks are inferred to be controlled principally by Fe/Mg ratio in the fluid or the bulk rock and by temperature. Compositional variations of “chlorites” in low-grade rocks, which appear to correlate with temperature or metamorphic grade, more likely reflect variable proportions of mixed-layered components. The assemblages of trioctahedral phyllosilicates tend to occur as intergrown discrete phases, such as chlorite-corrensite, corrensite-smectite, or chlorite-corrensite-smectite. A model for the corrensite crystal structure suggests that corrensite should be treated as a unique phase rather than as a 1:1 ordered mixed-layer chlorite/smectite.
138 citations
Cites background from "Some Interstratified Clay Minerals ..."
...It also forms by hydrothermal alteration of basaltic or ophiolitic rocks (Alietti 1958; Furbish 1975; Evarts and Schiffman 1983; Brigatti and Poppi 1984 a; Alt et al. 1985; Bettison and Schiffman 1988) and weathering of basic igneous rocks ( Smith 1960 ),...
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TL;DR: A B S TR A C T: The soils of Scotland are relatively young, being developed mainly on glacial drift deposited some 10, 000 years ago as discussed by the authors, but only a small number of genetic soil types are represented, but this is more than compensated for by the wide variety of parent materials from which the drift ultimately derives.
Abstract: A B S TR A C T: The soils of Scotland are relatively young, being developed mainly on glacial drift deposited some 10 000 years ago. Only a small number of genetic soil types are represented, but this is more than compensated for by the wide variety of parent materials from which the drift ultimately derives. The major parent materials include granite and granitic gneiss, gabbro, basalt/andesite, mica-schist and related metamorphic rock types, Lower Palaeozoic greywackes and shales, Old Red Sandstone sediments, Carboniferous sediments, fluvioglacial sands and gravels, and estuarine silts and clays. The clay mineralogy of the soil associations developed on these parent materials is described and the origin of the clay minerals is interpreted. It is concluded that the influence of inheritance is predominant, but that the effects of pre glacial weathering and Holocene pedogenesis can also be discerned. Inheritance has contributed a wide variety of clay minerals to the soils, including illite, kaolinite, chlorite, smectite and a number of interstratified minerals, pre-glacial weathering has resulted in the widespread formation of kaolinite and halloysite, irrespective of soil parent material or drainage class, and recent pedogenesis has brought about the transformation of inherited layer silicates by vermiculitization processes, with concomitant interlayer alumination, particularly in surface horizons.
65 citations
TL;DR: The fine-sand fraction (0·2-0·02 mm) was selected for the purpose of determining relative stabilities of the primary minerals under weathering conditions as discussed by the authors.
Abstract: Summary
The weathering of several basic igneous rocks of Lower Carboniferous age has been studied by optical microscopy and X-ray techniques. Although similar in mineralogy, the rocks have different textures and the fine-grained ones are most resistant to physical disintegration. In every rock, olivine has been affected by hydrothermal alteration to produce layer lattice silicates. The weathering of these products and the other mineral constituents of the rocks is described.
The fine-sand fraction (0·2-0·02 mm.) was selected for the purpose of determining relative stabilities of the primary minerals under weathering conditions. In order of increasing stability, the arrangement is labradorite, augite, magnetite, ilmenite, and hematite. The silt (0·02-0·002 mm.) and clay (< 1.4 μ) fractions contain saponite and/or vermiculite depending mainly on the weathering conditions of augite and felspar. Kaolin is present in both size fractions but illite is scarce. The cation-exchange capacity (c.e.c.) of both silt and clay fractions is consistent in most cases with the layer lattice silicate contents.
21 citations
TL;DR: In this article, a regular mixed-layer talc-saponite mineral, contaminated with a certain amount of orthochrysotile, was identified by several methods in the weathering products of a serpentinite rock from Ferriere, Nure Valley (Piacenza Province, northern Italy) and belonging to the “ophiolitic formation of the Italian Apennines.
Abstract: A regular mixed-layer talc-saponite mineral, contaminated with a certain amount of orthochrysotile, was identified by several methods in the weathering products of a serpentinite rock from Ferriere, Nure Valley (Piacenza Province, northern Italy) and belonging to the “ophiolitic formation” of the Italian Apennines. The structural formula of the mineral is: [Mg2.80 Fe
0.09
2+
Fe
0.20
3+
] [Fe
0.07
3+
Al0.45 Si3.48] O10 (OH)2 Mg0.006 Ca0.02 Na0.01 Electron microscopy enables the chrysotile fibres to be distinguished from the platy particles of the talc-saponite mineral. The infra-red method proved very suitable for identifying the talc and saponite constituents of the mixed-layer mineral. The thermal analyses (d.t.a. and d.t.g.) are valuable in revealing the mixed-layer character of the mineral.
19 citations