Identification and Crystalline Structure

6 CHARACTERIZATION OF SILICATE MINERALS 8.6.1 Identification and Crystalline Structure 

Besides XRD, other important studies are elemental analysis, either by chemical or physical methods, such as neutron activation analysis (NAA), x-ray fluorescence (XRF), or x-ray energy dispersive spectroscopy (X-EDS), for example (see Sections 7.6.1, 7.3.3, and 7.5.2, respectively) the advantage of these methods is that they are non destructive, as oppossed to wet chemical analysis. Additionally, IR spectroscopy can bring useful complementary information. Sometimes, the chemical composition is required along XRD analysis to fully identify a mineral. Also, thermal analysis (Section 7.6.5) is a useful tool in the qualitative and, sometimes, quantitative determination of clay minerals. 

Other important characterization studies are ion-exchange capacity, especially cationic, and specific surface measurement. CEC is an important parameter in clay characterization and soil behavior, because it affects nutrient availability, among other soil properties. Some clay minerals (smectites and vermiculites) have a high 

FIGURE 8.25 Simplified scheme of the procedure for XRD identification of clay minerals, showing the XRD patterns resulting for a hypothetical mixture of smectite (S), chlorite (C), vermiculite (V), illite (I), and kaolinite (K). (Reprinted from Amonette, J.E., Soil Mineralogy with Environmental Applications, Soil Science Society of America, Madison, WI, 2002, with permission). 

as exemplified in Table 8.3, due to permanent negative charge. On the other hand, anion-exchange capacity is generally low and present only at low pH values. The determination of CEC has been widely described in the literature (Sumner and Miller 1996 Zelazny, He, and Vanwormhoudt 1996 and references therein). 

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