Gemstones that begin with the letter "T"

Gemstone	Crystal System	Density	Hardness	Refractive index	Treatments
Tanzanite	orthorhombic	3.30	6.0-7.0	1.690-1.700	heat
Tiger-eye	microcrystalline	2.64-2.71	7.0	1.540-1.550	bleaching w/ honey tigereye
Topaz	orthorhombic	3.53	8.0	1.619-1.627	blue is irradiated
Tourmaline	trigonal	3.06	7.0-7.5	1.624-1.644 (green)	heat
Tsavorite	cubic	3.84	6.5 - 7	1.73 - 1.75	none
Turquoise	triclinic	2.73	5.0-6.0	1.610-1.650	dying, sealing