Gemstones that are Red.

Gemstone	Crystal System	Density	Hardness	Refractive index	Treatments
Alexandrite	orthorhombic	3.72	8.5	1.746-1.755	none
Beryl	hexagonal	2.72	7.5-8.9	1.577-1.583	heat, radiation, fracture filling, oiling
Coral	trigonal	2.65	3.5-4.0	1.486-1.658	dying
Corundum	trigonal	4.00	9.0	1.762-1.770	none
Diamond	cubic	3.52	10	2.417	radiation, drilling, fracture filling
Eudialyte	trigonal	2.8-3.0	5-51/2	1.598-1.602	none
Garnet	cubic	3.40	5.5-6.5	1.700-1.746	none
Hackmanite	cubic	2.29	6.00	1.483-1.487	none
Kunzite	monoclinic	3.18	6.0-7.0	1.660-1.676	light will fade
Morganite	hexagonal	2.72	7.5-8.0	1.577-1.583	radiation
Rhodolite	cubic	3.84	7.0-7.5	1.760	none
Ruby	hexagonal	4.00	9	1.762-1.770	heat, fracture filling
Spinel	cubic	3.60	8	1.718	none
Tourmaline	trigonal	3.06	7.0-7.5	1.630-1.662(red)	heat