Calculation of Electrostatic Interlayer Bonding Energy and Lattice Energy of Polar Phyllosilicates: Kaolinite and Chlorite

P. Hartman
Instituut voor Aardwetenschappen, Rijksuniversiteit Utrecht, Postbus 80021, 3508 TA Utrecht, the Netherlands

Abstract: The electrostatic lattice energy of polar phyllosilicates can be calculated when a correction term Ecorr equal to −2πµ2/V is taken into account, where µ is the dipole moment of a slice d(001) and V is the molecular volume. The interlayer bonding energy can be obtained by Giese's method, if the energy of separation of the layers over a distance Δ is plotted againts 1/[d(001) + Δ]. Thus, for a polar chlorite the interlayer bonding energy is 69.8 kJ/unit cell. Using the Madelung method, the interlayer bonding energy of slices of kaolinite having a thickness of d(001) is 84 kJ/mole. Similarly the interlayer bonding energy of slices having a thickness d(020) is 2520 kJ/mole. To avoid the instability of the outer slices of the crystal caused by the cooperating dipole moments of all slices, the hypothesis was made that the atoms have in reality reduced charges and that the charge reduction is such that the dipole moment becomes zero. The adopted charges lower the interlayer bonding energy to as little as 14 kJ/mole. The interlayer interaction of slices of fluorkaolinite with thickness d(001) is repulsive. Crystals of a polar chlorite must be bounded either by incomplete hydroxide layers or by layers onto which charge-compensating anions are adsorbed. Polarity makes cleavage in chlorite more difficult.

Key Words: Chlorite • Electrostatic energy • Interlayer bonding • Kaolinite • Lattice energy

Clays and Clay Minerals; June 1983 v. 31; no. 3; p. 218-222; DOI: 10.1346/CCMN.1983.0310307
© 1983, The Clay Minerals Society
Clay Minerals Society (www.clays.org)