The structure of multilayer polytype modifications of layer silicates may be regarded as the result of a combination of regularly oriented single layers. Accordingly, the optical constants of a single layer (of a monolayer polytype modification) may be used for the calculation of optical constants of any other multilayer polytype modification of a given type of layers.
The formulas connecting the constants of a polytype modification of layer silicates have enabled the establishment of the main parameters (Ng, Nm, Np, 2V) of the muscovites 1M and 2M2 according to the known optical constants of the muscovite 2M1, and the computation of the new constants of kaolinite and nacrite based on the known parameters of dickite. The optical constants established theoretically were confirmed by direct measurements for muscovite 1M, muscovite 2M2 (gämbelite) and kaolinite. The optically positive character of kaolinite with +2V = 25° has been established.
The assumption of the optical mixibility of finely dispersed polyminerallic media, in which the dimensions of monotype crystals are smaller than the visible light waves, made it possible to determine the quantitative relations of clay minerals in the mixtures based on optical constants of oriented aggregates.