## Abstract

This paper presents an original and useful method for calculating and comparing the electrostatic component of the lattice energies of families of related, complex structures. The methodology and use of hypothetical, tractable steps in passing from one structure to another can be extended to families of crystal structures other than the phyllosilicates. Calculations made on a single `generic' silicate, KX<latex>$_{2}$</latex>X<latex>$^{\prime}$</latex>T<latex>$_{4}$</latex>O<latex>$_{10}$</latex>(OH)<latex>$_{2}$</latex>, enables us to obtain the lattice energies of 1M aluminium mica, phlogopite, talc, pyrophyllite, saponite, beidellite, illite, montmorillonite and hectorite and their fluorinated analogues. Site potentials are readily obtained when calculations are made in this manner. Considerable saving of computer time and effort coupled with little sacrifice of accuracy are a feature of this approach. The paper further goes on to suggest how comparison of this type of generic calculation with the results obtained from calculations made on the true individual phyllosilicate structure can extend the potential information that can be gained from these studies. The investigation of substitutional and relaxation energies of the phyllosilicates is considered. Surface energies (shown to be quadratic functions of x for micas derived from the structure A<latex>$_{x}$</latex>X<latex>$_{2}$</latex>X<latex>$^{\prime}$</latex>T<latex>$_{4}$</latex>O<latex>$_{10}$</latex>(OH)<latex>$_{2}$</latex>, (A = Na or K)) are calculated on the same principle, from, in this case, a `generic' expanded lattice. The transferability principle introduced in this work enables us to make specific predictions regarding minerals for which single crystal X-ray diffraction studies are impractical. We attempt wherever possible an interpretation of the energies we calculate.