Gem in Diablo Ⅲ

There are four gem types that can be collected throughout Sanctuary. These include topaz, emerald, ruby, and amethyst. They can be found in differing qualities; the highest quality that can be found is the flawless square, which will not be seen until inferno mode. There are 15 different qualities ranging with bonuses of +6, to +62 for base stats including intelligence for topaz, strength for ruby, dexterity for emerald, and vitality for amethyst when put into any item that is not a weapon or helm. When put into a helm the bonuses include a percent life increase for amethyst, a percentage of extra gold from monsters for emerald, a percentage of bonus experience points for ruby, and a percentage of better magic find for topaz. 

Gems can be combined at the Artisans to make higher level gems, to increase the bonus they give to items they are mounted in. The mounting processes is reversible, and gems can be removed for a price with the gem crafter Covetous Shen. A gem can also be removed by salvaging the item it is mounted in, and the gem is left in the character's inventory.