Thin section of mica. Polarised light micrograph of micaceous minerals (a group of silicate minerals) within a thin section of mica. Mica would normally display perfect cleavage, the tendency to split along definite crystal planes. This is because the flakes of mica from which it is comprised show parallel alignment. Here this is not the case, and brightly-coloured flakes of muscovite, the most common mica mineral, show a wavy pattern. Biotite can also be seen in brown hues. The alignment of the flakes is down to the deformation forces of the rock that accompany the formation of the mica. Magnification: x2.9 when printed 10 centimetres wide.