The use of X-ray texture analysis techniques enables a simplified picture of the microstructure of a rock to be built up. In this thesis it is shown that, in spite of a wealth of evidence on pre-failure rock behaviour, a simple application of Griffith theory to the assumed microstructure can provide an adequate description of the failure characteristics of an anisotropic rock. It is suggested that the crystallite structure within the rock controls the pre-failure activity in such a way as eventually to produce the crack formation initially deduced from that crystallite structure. These conclusions are drawn from work done on two rocks of different character, Penrhyn Slate and Lumley Mudstone
