Gemstones that begin with the letter "S"

Gemstone	Crystal System	Density	Hardness	Refractive index	Treatments
Sapphire	hexagonal	4.00	9	1.762-1.770	heat, fracture filling
Smoky Quartz	hexagonal	2.66	7.0	1.544-1.553	none
Spinel	cubic	3.60	8	1.718	none