Fig. 1.

Phyllosilicate structures and ripplocation morphology. a–c Atomic structure models of some common phyllosilicates with valences identified by polygons. The indices of these polygons are occupied by O atoms or OH groups. a Biotite, like other micas, requires an interlayer cation (I) to balance the overall negative charge of its tetrahedral (T) and octahedral (M) layers. In the cases of biotite and muscovite this cation is predominantly K, whereas in paragonite, and others, it is Na. b Lizardite, like the other serpentine minerals antigorite and chrysotile, has a 1:1 ratio of T to M layers, which possess a neutral charge resulting in no interlayer cations. c The structure of chlorite is similar to biotite except that the interlayer cations are replaced by individual octahedral layers, so called brucite like sheets. d, e Comparison between a dislocation (d) and a ripplocation in a generic phyllosilicate lattice (e). Both enable the movement of one plane of atoms over another. However, while dislocation climb is required to deform out of this plane in d, ripplocations intrinsically contain an element of c-axis parallel strain due to bending and more crucially are attracted to each other rather than repelled