Appl Note 105

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Powder Diffraction of Clays and Clay Minerals



Clays and clay minerals are a special class of silicate minerals commonly with  disordered structures. The crystal structures of many clay minerals (Space group, x,y,z coordinated of atoms), are not well defined due to disorder and flexibility of the structures. X-ray powder diffraction pattern of most of clay minerals are site-specific. However, there are well investigated and documented in scientific papers and books describing the powder patterns of clay minerals, which could be used for identification purposes. Separation of clays from soils and  other minerals, as well as preparation of clay minerals for diffraction studies are requiring special techniques.

Clay Minerals Society Links Page
A very extensive set of links which is slanted towards the analysis of clay minerals but also includes lots of more general crystallography, crystal chemistry, X-ray diffraction links and geological links. There are links to some great Earth Science sites here (and Dilbert too). Maintained by Steve Chipera of Los Alamos National Lab.


Clay minerals

Clay is a generic term for an aggregate of hydrous silicate earth particles less than 4 micrometers in diameter. They are generally formed by the chemical weathering of silicate-bearing rocks by carbonic acid, but some are formed by hydrothermal activity. Clays are distinguished from other small particles present in soils such as silt by their oblong shape, affinity for water and high plasticity index.

There are three main groups of clays: Kaolinite-Serpentine, Illite, and Smectite. Altogether, there are about thirty different types of "pure" clays in these categories, but most natural clays are mixtures of these different types, as well as other weathered minerals.

Description of clay minerals


Sample Preparation

Sample preparation techniques of clay minerals well discussed in


Phase Identification

Flow diagram for clay mineral identification


Phase Quantification

Other Application Notes are also available:


Note No



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