group garnet system isometric formula Ca3Cr2(SiO4)3 optic uniaxial - biaxial Too-Vee 0 - 90¡ relief.1 high pos min. index 1.838 / 1.870 color colorless pleochroism no birefringence.1 anomalous cleavage no elongation no extinction *** angle *** alteration chlorite, hornblende, epidote, and iron oxides habit.1 euhedral occurence igneous (peridotite) TwoV 1 2 relief 3 pleochroism.2 birefringence cleavage.2