Anisotropy of frictional forces in muscovite mica

The static and dynamic frictional forces of single-crystal muscovite mica are measured as a function of the lattice misfit angle between the two contacting cleavage lattices at a very light load under both dry and ambient atmospheres. The frictional forces are anisotropic with respect to the lattice misfit angle, i.e., they increase (decrease) when the contacting surfaces approach being commensurate (incommensurate). The underlying mechanisms of the anisotropy are discussed in terms of the commensurability between the contacting lattices.