Diablo 4 - All Gems And Bonuses

gamespot.com:

Gems are one of the many returning features in Diablo 4. These items slot into certain pieces of armor, jewelry, and weapons to give them added bonuses, depending on what you slotted them into. Not all equippable items that you find or purchase will have a gem socket, but you can pay a fee at a gem shop to add a single socket to that item if you wish. You can find gems as lootable drops from killing mobs, bosses, and opening chests.

In Diablo 4, there are five different rarity levels that a gem can come in. The lowest level will give your item a small buff while the highest level will provide a much larger buff. The gems will also give different bonuses depending on if you slot it into a piece of armor, jewelry (amulet or ring), or a weapon (one-handed or two-handed). To see all of the available gems and what bonuses they give each item in Diablo 4, check out the guide below.

For the most part during your run through the main story of Diablo 4, you will only see the Crude or Chipped variety of gems as lootable drops. Crude is the lowest level a gem can come in, and you are able to upgrade it to a Chipped gem by visiting a gem vendor and trading three Crude gems to obtain a single Chipped one. From here, you need to reach a higher level (it's unclear what level) and you will be able to trade three Chipped gems to obtain a single regular gem.

After this, you can repeat the same process to obtain a Flawless and Royal gem, but those are not available until after you have beaten the main story with a character in Diablo 4. Below, we will list all of the different gems, their varieties, and their bonuses so you can see exactly which ones will work best for your build.

Crude Amethyst

Chipped Amethyst

Amethyst

Flawless