group garnet system isometric formula Mn3Al2(SiO4)3 optic isotropic Too-Vee no relief.1 high pos min. index 1.790 / 1.810 color colorless pleochroism no birefringence.1 no cleavage no elongation no extinction no angle no alteration chlorite, hornblende, epidote, and iron oxides habit.1 euhedral occurence igneous (granitic,pegmatite, felsic), metamorphic (high grade Mg-rich) TwoV relief 3 pleochroism.2 birefringence cleavage.2