0 a jewel (= precious stone), especially when cut into a regular shape: --
The rings have coloured gemstones surrounded by diamonds.
Blue diamonds are rare and sought-after gemstones.
He took one of the gem stones out and held it against the light.
I would recommend this book as a general text on the geologic occurrence of gemstones.
The piece is made with more than eleven hundred gemstones, including rubies, sapphires, and emeralds.