Crystallographic and optical characteristics of crystal habits have been investigated comparing the both results of goniometric and newly developed polarizing microscopic methods. It has been found that the predominant faces of crystal habits are mostly formed by (001) or (100) of orthorhombic or monoclinic system and (010) of monoclinic system, and a little part by triclinic (001). Not so many numbers of predominant faces were found to be formed by orthorhombic or monoclinic (110) making prismatic habits. Key refractive indices have been found to be uniquely measured from those habits, and it was also found that one or two of them were coincided with the principal refractive indexes, which will become important facts for the analytical use of crystal habits.