These features are commonly seen in thin section in plane or cross polars; they may or may not reflect crystallography (zoning does, deformation can). There is much to be learned from these features about the minerals themselves (and clues to their identification) and about the rocks which they comprise.
� Plagioclase(movie, next set of pictures), amphibole (following), quartz (last) examples illustrating twinning, habit, cleavage, zoning, inclusions, and alteration.