Crystalline clay

The development of apparatus and techniques, such as x-ray diffraction, contributed gready to research on clay minerals. Crystalline clay minerals are identified and classified (36) primarily on the basis of crystal stmcture and the amount and locations of charge (deficit or excess) with respect to the basic lattice. Amorphous (to x-ray) clay minerals are poody organized analogues of crystalline counterparts. 

In addition to the crystalline clays described earlier, there are some materials that act like clays but do not have crystalline structure. Amorphous clays do not have a definite X-ray diffraction pattern and are differentiated from the crystalline clays on this basis. They are composed of mixtures of alumina, silica, and other oxides and generally have high sorptive and cation exchange capacities. Few soils contain large amounts of amorphous clays [2],... 

Schwertmann, U. Cambier, P. Murad, E. (1985) Properties of goefhites of varying crystallinity. Clays Clay Min. 33 369-378 Schwertmann, U. Carlson, L. Fechter, H. (1984) Iron oxide formation in artifidal groundwaters. Schweiz. Z. Hydrol. 46 185— 191... 

Taylor, R.M. (1984) Influence of chloride on the formation of iron oxides from Fe(ll) chloride. Effect of (Cl) on the formation of lepidocro-cite and its crystallinity. Clays Clay Min. 32 175-180... 

A definite prediction of DLVO theory is that charge-stabilized colloids can only be kinetically, as opposed to thermodynamically, stable. The theory does not mean anything at all if we cannot identify the crystalline clay state (d 20 A) with the primary minimum and the clay gel state (d 100 to 1000 A) with the secondary minimum in a well-defined model experimental system. We were therefore amazed to discover a reversible phase transition of clear thermodynamic character in the n-butylammonium vermiculite system, both with respect to temperature T and pressure P. These results rock the foundations of colloid science to their roots and... 

Schwertmann, U, Cambier, P. and Murad, E. (1985) Properties of goethites of varying crystallinity. Clays Clay Min. 33 369-378. 

Kaolinite, on the other hand, has no structural counterpart among the igneous minerals. It is also the most widespread of the crystalline clay mineral. The most likely mechanism for kaolinite formation is the complete breakdown of feldspar or mica particles and the precipitation of kaolinite from Al(OH)3 and Si(OH)4 from the soil solution or from amorphous, less stable intermediates. 

Soil Various natural clays Cu, Pb, Zn Spiked Heavy metal migration dominated by crystalline clay minerals lowest efficiency humic-aUophanic and allophonic soils Darmawan and Wada (2002)... 

Allophane Allophane is an amorphous clay from natural soil it is a natural aluminosilicate originating from the transformation of volcanic ashes and glasses with weathering. Allophane exists for young volcanic soil and is progressively transformed into crystalline clays, halloysite, then into kaolinite... 

Osorno and San Patricio soils are Andepts with a high organic matter content dominated by variable surface charge inorganic components (Table 1). On the other hand, Collipulli soil is an Ultisol with low organic matter content, dominated by crystalline clay minerals with little or no variable surface charge. 

After 1950 the application of such methods by workers in Japan (Aomine and Yoshinaga [1955]) and New Zealand (Birrell and Fieldes [1952]) showed that certain ando soils from volcanic ash in Japan and in New Zealand all classes of both yellow-brown pumice soils derived from rhyolitic volcanic ash and yellow-brown loams derived from andesitic and from rhyolitic volcanic ash had clay fractions composed predominantly of allophane (Fieldes [1953, 1955]). The ability to obtain allophane relatively free from crystalline material and the high proportions in Japan and New Zealand of agriculturally important land derived from volcanic ash encouraged the study and elucidation of the properties of allophane in both countries at an early date. Subsequent work in other countries confirmed that allophane was a common constituent of volcanic ash soils. Allophane was also shown to be present in high proportions in clay fractions of weakly developed soils derived from basalt (Fieldes [1953]) or from other basic rocks (Mitchell and Farmer [1962]). In addition, in recent years serious attention has been given to the more difficult problem of assessing amounts of allophane in the presence of crystalline clay constituents in soils of many different kinds (Mitchell and Farmer [1962]). 

Electron microscopy can also detect amorphous material in soils containing crystalline clay minerals. Fieldes and Williamson [1955] detected small quantities of amorphous matter in the electron micrographs of most of the soil clays they described. Similar features probably would be visible in soils such as those described by Mitchell and Farmer [1962] from Scotland. The electron microscope is a very useful tool for examining the fine detail of the clay fraction of soils, but care should be taken because of the changes that can take place with different treatments, as has been shown above. 

The presence of a large endothermic peak in the absence of montmorillonite-saponite minerals is usually indicative of the presence of noncrystalline aluminosilicate gels furthermore, such materials, unlike the crystalline clay minerals, are capable of rehydration after being heated to 600°C (Mitchell and Farmer [1962]). Mixtures of kaolinite and illite are difficult to interpret, since the principal peaks usually overlap, but attention to detail, especially in the low-temperature and high-temperature regions of the curve, can often give a clue as to the minerals present. 

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