HYPERBOLIC AND ELLIPTIC LAYER WARPING IN SOME SHEET ALUMINOSILICATES

The curvature of alumino-silicate structures related to imogolite and kaolinite is investigated using techniques derived from differential g eometry and topology. It is demonstrated that the curvatures of these structures can be varied to give a limited range of ''modulated'' rela tives, of both hyperbolic and elliptic curvature. These modulated stru ctures may account for a number of soil minerals, the ''poorly ordered non-crystalline aluminosilicates'' (Wilson et al. 1988), including pr otoimogolite and allophane.