CLEAVAGE AND STRAIN ELLIPSOID Commonly in plane of maximum extensions. The cleavage is parallel to he l1l2 plane of the finite strain ellipsoid, unless it fails physically to rotate parallel to this plane. Flattening of strain ellipsoid or perpendicular to direction of maximum shortening. If the principal strains are l1>l2>l3, then foliation forms parallel to the l1l2 plane or normal to l3. A pole to cleavage normally is in the direction in which the rock is maximally shortened. This precludes that exclusively prolate or dominantly prolate strain will give rise to very discrete foliation or cleavage planes. Cleavage planes of micas tend to become aligned in the XY plane of the finite strain ellipsoid
