Two-dimensional lattice images of stacking disorder in wollastonite

Two-dimensional lattice images of low-temperature triclinic wollastonite (-CaSiO₃) indicate that two types of stacking disorder occur: (1) simple stacking faults and (2) twinning which also involves displacement in the composition plane. Both types of defect produce very similar structures with monoclinic symmetry (parawollastonite). Dislocations are involved at the termination of lamellae of parawollastonite in a triclinic matrix and a model for the dislocation core is proposed.Now at the Edward Davies Chemical Laboratories, Aberystwyth, SY23 1NE, U.K.