Abstract: Grunerite asbestos (var. amosite) from Penge, Transvaal, contains lamellae consisting of multiple-chain I-beams which frequently terminate within the structure. Such terminations may be either coherent or incoherent, the latter involving disturbances of the structure akin to dislocations. These may be of the nature of edge dislocations or of dislocations having both edge and screw components.
Models are presented which have been used to elucidate the structural disturbances associated with the termination and side-stepping of multiple-chain lamellae. Odd-multiple-chains are shown to be of particular significance in giving rise to dislocations with a screw component along the c-axis.