group garnet system isometric formula Mg3Al2(SiO4)3 optic isotropic Too-Vee no relief.1 high pos min. index 1.720 / 1.770 color colorless pleochroism no birefringence.1 no cleavage no elongation no extinction no angle no alteration chlorite, hornblend, epidote, and iron oxides habit.1 euhedral occurence ignoeus (ultramafic, kimberlite), metamorphic (high grade) TwoV relief 3 pleochroism.2 birefringence cleavage.2