What is the difference between tanzanite and azurite?

tanzanite is di-chronic gemstone having blue and violet colors. it have specific gravity of 3.4 and refractive index of 1.7 . it's have 6.5-7 hardness, sometimes it's have columns striations. while azurite have dark blue to purple color . it's have specific gravity of 3.7 and refractive index of 1.83 . it's have 4 hardness at moh's scale.