In many occurrence of biotite in igneous and metamorphic rocks, chlorite is intergrown with the biotite in textures that indicate the chlorite has formed as a replacement of biotite that formed at an earlier time.  In A, pale green chlorite occurs along the {001} cleavage planes of the tan biotite (which contains abundant pleochroic halos).  In B, the relationship between chlorite and biotite is similar, with a major portion of the centre of the biotite grain occupied by chlorite.  The chlorite contains inclusions of titanite along the {001} planes of the chlorite, whereas the biotite shown here (and elsewhere in the same rock) does not contain titanite. This suggests that the bioitite is titanium-rich and the titanium could not be accommodated in the secondary chlorite so formed a separate Ti-rich phase (titanite).  A is from a kyanite schist from Fernleigh, Ontario and B is from a granite from an unknown location.  Fields of view are 5.5 mm across in A and 2.2 mm across in B.  Both photographs were taken in plane polarized light.