X‐ray diffraction studies on the arrangement of water molecules in a smectite. I.Homogeneous two‐water‐layer Na‐beidellite

A method of indirect analysis of X‐ray diffraction patterns of homogeneous hydrated microcrystalline silicates is introduced. This method is applied to a sodium beidellite of Rupsroth, Bavaria, Germany, hydrated with two water layers to determine all its structural characteristics: namely, the average dimension and size distribution of coherent domains, stacking mode of the layers along the c * direction, levels and number per unit cell of water molecules. A critical analysis on the `concept of homogeneity' of hydrates and a discussion on the conditions of its application to lamellar microcrystalline silicates with a few numbers of layers are made.