Chlorite clay origin

The most common type of mixed-layer clay is composed of expanded, waterbearing layers and contracted, non-water-bearing layers (i.e., illite-montmorillonite, chlorite-vermiculite, chloritc-montmorillonite). Most of these clays form by the partial leaching of K or Mg (OH)2 from between illite or chlorite layers and by the incomplete adsorption of K or Mg(OH)2 on montmorillonite- or vermiculite-like layers. They most commonly form during weathering or after burial but are frequently of hydro-thermal origin. 

Clays are aluminosilicates with a two-dimensional or layered structure including the common sheet 2 1 alumino- and magnesium- silicates (montmorillonite, hectorite, micas, vermiculites) (figure 7.4) and 1 1 minerals (kaolinites, chlorites). These materials swell in water and polar solvents, up to the point where there remains no mutual interaction between the clay sheets. After dehydration below 393 K, the clay can be restored in its original state, however dehydration at higher temperatures causes irreversible collapse of the structure in the sense that the clay platelets are electrostatically bonded by dehydrated cations and exhibit no adsorption. 

Ryan, P. C., and R. C. Reynolds. 1997. The chemical composition of serpentine/chlorite in the tuscaloosa formation, Unites States Gulf Coast EDX vs. XRD determinations, implications for mineralogic reactions and the origin of anatase. Clays Clay Miner. 45 339-352. 

Clays are volumetric ally the most abundant mineral group in coal. They can be authigenic or detrital in origin. Kaolinite is the most common clay and the most common authigenic mineral in coals. The silicon and aluminum in kaolinite are, perhaps, residual from the dissolution of ferromagnesian minerals and feldspars. Illite and mixed layer clays in coal are almost exclusively detrital in origin. Chlorites, smectites, and other clay minerals may be abundant locally. 

Geologically and genetically, clay minerals are difficult to define simply and adequately, but broadly they are layer lattice silicates of secondary origin. In the same classification are the micas, talc, chlorites, and serpentines which are not strictly clay minerals. In this context, secondary origin means that mineral formation has arisen from the weathering of primary or igneous rock, e.g. granites and basalts. 

Soil Mg originates from the decomposition of minerals such as dolomite, biotite, olivine, serpentine, and chlorite. Soluble Mg may be held in the exchangeable form on soil clays or organic matter. 

Chlorite replaces kaolinite, clay pseudomatrix, infiltrated clays, micas and heavy minerals. It occurs as rims composed of platelets oriented perpendicularly to grain surfaces. The rims were formed by replacing infiltrated smectitic clay coatings, which were originally oriented tangentially to grain surfaces (Fig. 14A) (see Moraes De Ros, 1990). These infiltrated clays were presumably introduced into the vadose zone of alluvial continental sediments under semi-arid conditions by episodic floods (Walker et al., 1978 Moraes De Ros,... 

Typically, mechanically infiltrated clays are originally detrital smectites formed under semi-arid weathering conditions (see Keller, 1970 Walker et al., 1978). This is evidenced by the dominance of smectitic clays in the mudstone samples and in the mud intraclasts. Infiltrated coatings and derived chloritized rims are conspicuous, particularly in medium-grained sheet-flood sandstones (up to 2.7 vol%). 

Intergranular zones occupied by glassy material are frequently observed (Fig. 6). This process produces abundant clay minerals. Montmorillon-ite, chlorite and a small amount of celadonite were determined by XRD. In other sectors isotrope material, (considered relictic from the original pal-agonite) was observed. Apatite is abundant. 

Peach. A term used by Cornish miners, originally for chlorite, but latterly applied to veins of quartz and schorl forming part of the waste from china-clay pits. 

Slates are related to clays. The DTA technique has been applied to study the weathering quality as well as an aid to the identification of slate of unknown origin. Figure 17 shows the differential thermal analysis of samples of roofing slate of three different qualities.The first curve represents a slate of excellent durability. The peaks at 610 and 850°C may be due to some type of chlorite. The inflection at 575 C is caused by the presence of quartz. In the calcined material (2 curve), the presence of quartz is more clear. The third curve is obtained with a slate that was found in practice to delaminate slowly on roofs under conditions of low atmospheric pollution. The poor durability may be caused by the slow oxidation of pyrite in the slate and subsequent reaction between the oxidation product and calcite to form calcium sulfate. The presence of pyrite and calcite is indicated by the peaks at 450° and 770°C, respectively. The fourth curve of slate of pure quality is dominated by the large calcite peak. The exothermic peaks at 930° and 420°C suggest the presence of chlorite and a small amount of pyrite, respectively. 

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