Violet, Purple and Lilac colored Gems

Gemstone	Crystal System	Density	Hardness	Refractive index	Treatments
Amethyst	hexagonal	2.66	7	1.544-1.553	heating alters to citrine
Corundum	trigonal	4.00	9.0	1.762-1.770	none
Diamond	cubic	3.52	10	2.417	radiation, drilling, fracture filling
Garnet	cubic	3.40	5.5-6.5	1.700-1.746	none
Jadeite	microcystalline	3.34	6.5-7.0	1.660-1.680	dying
Kunzite	monoclinic	3.18	6.0-7.0	1.660-1.676	light will fade
Quartz	hexagonal	2.66	7.0	1.544-1.553	fracture filling
Sapphire	hexagonal	4.00	9	1.762-1.770	heat, fracture filling
Spinel	cubic	3.60	8	1.714-1.750	none
Tanzanite	orthorhombic	3.30	6.0-7.0	1.690-1.700	heat
Tourmaline	trigonal	3.06	7.0-7.5	1.630-1.662	Heat, radiation