Determination of Minor Contents of Smectite Layers in the Dispersed Dioctahedral K-bearing Micaceous Minerals of the Illite, Aluminoceladonite, and Glauconite Composition

Abstract

A theoretically substantiated technique has been elaborated for the precise determination of minor contents of smectite layers in the dioctahedral mixed-layer structures with a disordered alternation of K-bearing micaceous and ethylene glycol-saturated smectite layers. It is shown that observed positions of the possible mixed-layer mica–smectite structures in the d(003)obs–d(007)obs or 2θ(003)obs–2θ(007)obs diagrams are distributed along a set of parallel straight lines. Data points of each straight line correspond to the mixed-layer structures with one and the same content of smectite layers. A complete matching of theoretical model was recorded in the positions of d(003)obs–d(007)obs and 2θ(003)obs–2θ(007)obs pairs of the basal reflections determined in diffractograms simulated for 160 two-component mixed-layer mica–smectite structures differing in the thickness of alternating layers and their relative content. We studied samples of the dioctahedral K-bearing micas of the glauconite, illite, and aluminoceladonite composition with different thickness of micaceous layers. Positions of the mixed-layer structures of the studied samples on the 2θ(003)obs–2θ(007)obs and d(003)obs–d(007)obs plots make it possible to visually determine the content of smectite layers in each structure accurate to 0.5%. The content of smectite layers in the studied samples varied from 2 to 15%. We obtained equations relating the thickness of smectite and micaceous layers for a specified content of smectite layers. They make it possible to determine the thickness correlation between specified mica and smectite layers. Analogous equations can be used to calculate the Wsm value in each sample for specified experimental values of d(001)mc and d(001)sm and d(003)obs or d(007)obs. The Wsm values coincide within an error limit of 0.2% with those based on the visual estimates in plots.