Gemstones that begin with the letter "P"

Gemstone	Crystal System	Density	Hardness	Refractive index	Treatments
Pearl	organic	2.70	2.4-4.0	1.530-1.685	dying,bleaching
Peridot	orthorhombic	3.34	6.5-7.9	1.654-1.690	none
Pyrite	cubic	5.00	5.0-6.5	2.940-3.220	none