About twelve miles south-east of Burghersdorp in the Cape Province, South Africa, the unusual clay reported in this paper was first discovered on the farms 'Groenvlei' and 'Kuilfontein'. Later deposits were also uncovered on the farms 'Kapokkraal' and 'Kleinhoek'.The clay-mineral appears to be of a very unusual type, namely, a regular mixed-layer clay-mineral (1:1 hydrous mica and montmorillonite). The mode of origin of the clay is also of interest in that it appears to be produced from a shale by hydrothermal alteration, due to intrusion of dolerite sheets.
Six profiles taken from the dikeland areas of Nova Scotia rvere examined chemically and n-rineralogically. The mineralogy of the various layers was similar within and betrveen profiles, except that the reddish layers contained goethite rvhile the grey layers did not. The latter were very strongly acidic and had an unusually high organic matter content due to burial of undecomposed vegetation by tidal sediments. While they contained no goethite, they had a sienilicant amount of "free iron". It is nrooosed that where sufficient organic matter rv.rs available the grei/ laycrs'were produced by anaerobic bacterial reduction of the reddish iron oxides.Quartz was the predominant non-clay rnineral associated with mica, feldsoar and chlorite. The clav fraction consisted of illite with characteristics of rnuscovite, chlorite similar to "srvelling" chlorite, kaolinite and montmoril-INTRODUCTIOI{
INABSTRACT X-ray diffraction, differential thermal, chemical analysis and cation exchange data indicate a progressive genesis upon hydrothermal alteration of rhyolitic materials in an extensive fault zone. Kaolinite, a Ca-Mg beidellite, mixed-layer beidellite-hydrous mica and beidellite-vermieulite clay minerals, quartz, cristobalite and feldsp~ r commonly occur in the deposit.Detailed studies show that the sequence of the 2 ." 1 clay mineral alteration is beidellitehydrous mica mixed-layer -+ beidellite-vermiculito mixed-layer --> beideUite. This mineralogical change parallels a progressive decrease in the layer charge and amount of fixed K + present and an increase in exchangeable Ca + and Mg + respectively.
At the 4th International Soil Science Congress held in Amsterdam (1950) a special meeting discussed the nomenclature of clay minerals and suggested “hydrous mica” as a general term for those clay minerals that are neither well crystallised micas nor pure expanding minerals.In the past various names have been used for the hydrous micas. As early as 1912, Galpin, and later, in 1920, Bayley, introduced the terms “hydro-mica” and “hydrous mica” respectively, to designate a micaceous clay mineral. Since then, reports have been made of the presence in soils of a potash-bearing clay mineral (Wherry et al., 1929), and in clays of a mica-like clay mineral (glimmerartige Tonmineralien) (Endell et al., 1935), and a sericite-like mineral (Grim, 1935). In 1937 Grim et al., for the first time proposed the term “illite” as a “general term for the clay mineral constitutents of argillaceous sediments belonging to the mica group.” Other names include bravaisite (Ross and Hendricks) and sarospatite (Maegdefrau and Hofmann, 1937), but the validity of these as specific minerals is questionable since they have been found to exist as mixtures of hydrous micas and montmorillonoids (Bradley, 1945; Brindley, 1951).
X-ray diffraction and differential thermal analysis data are presented for colloid fractions from a soil and shales containing a vermiculite and a montmorillonoid; a chlorite and a vermiculite-chlorite mixed-layer mineral; and a montmorillonoid and a vermiculite-chlorite mixed-layer mineral. The minerals were identified by heating the clay fractions at various temperatures and by treating them with ethylene glycol and/or ammonium chloride.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.