group oxide
system hexagonal
formula Al2O3
optic uniaxial neg
Too-Vee 0¡
relief.1 high pos
min. index 1.758 / 1.794
color colorless
pleochroism yes
birefringence.1 0.008 - 0.009
cleavage no
elongation yes
extinction parallel, symmetrical
angle 0¡
alteration margarite, diaspore, gibbsite, alumnosilicates
habit.1 hexagonal, tabular
occurence igneous (kimberlites), metamorphic (high grade, contact, pelite)
TwoV
relief 3
pleochroism.2 blue, yellow, green
birefringence 1 4
cleavage.2 {0001} basal parting, {1011} rhomb parting