Micas, like the colorful muscovite in this photo, grow as flat plates. The mica plates tend to align themselves parallel to the direction of flow in a deforming rock, partly because they grow as the rock deforms. The planar fabric created by the parallel mica plates is called foliation or schistosity. Here you see the edges of the mica plates. Notice that there are two distinct foliations, almost at right angles to each other. This rock evidently had a life that involved at least two deformations.

Crossed polarizers