Obreimoff revisited: Controlled heterogeneous fracture through the splitting of mica

•When split with a smooth wedge, muscovite mica exhibits uniform fracture along a single cleavage plane.•Thickness of cleaved mica sheets determines required splitting force.•Sharp thickness contrasts (heterogeneities) result in higher splitting force than in homogeneous case.•Thickness contrast is analogous to compliance contrast, which may be useful in strongly-bonded layered ceramics.