Season of Witchcraft introduced a new type of Socketable called Occult Gems, which can be placed into items with sockets.
These provide several bonuses that can improve the builds of your characters but before you can craft them, you need to unlock their recipes using Grimoires.
Getting your hands on Grimoires can be done after you have progressed a bit in Season 7, allowing you to farm them later once you have progressed past the Penitent Difficulty.
How To Get Grimoires?
Obtaining Grimoires becomes possible once you have reached Torment I or higher difficulties as these World Tiers allow them to drop.
1) Whisper Caches
Completing Whispers and returning to the Tree of Whispers or interacting with the Raven of the Tree will provide you with Whisper Caches as rewards.
There is a chance that a Grimoire may drop when you open the Whisper Cache regardless of what World Tier you are on. (All rarities may drop starting from Torment I)
2) Headless Husks
Headless Husks bosses have a chance to drop Grimoires, and these enemies can be found during the Season of Witchcraft by uprooting Exposed Roots.
You may find Exposed Roots when you are exploring Headhunt Activity Zones or when you are running Roothold Dungeons.
How To Use Grimoires?
Once you have obtained a Grimoire, you may use it from your inventory (It will be in the Consumables Tab) to learn the recipe for the Occult Gem you want to craft.
This will consume the Grimoire that you had and if you check with Gelena (Coven Jeweler) and will find the recipe amongst the Occult Gems that may be crafted.
Crafting Occult Gems
Crafting Occult Gems can be done by speaking to Gelena (Coven Jeweler), who can be found at The Tree of Whispers.
If you have completed the Seasonal Quests, you may already be familiar with Gelena and will already have unlocked your first recipe.
Crafting Occult Gems will often require a Fugitive Head, Restless Rot, and a large amount of Gem Fragments depending on which one you will craft.
Verdict
Farming Grimoires can take up a lot of time if you don’t delve into the Seasonal Activities during Season of Witchcraft as there are mainly 2 ways to get them.
It would be a good idea to use up your Roothold Keys to complete Roothold Dungeons before grinding in the Headhunt Activity Zones.
Each Grimoire will unlock a specific Occult Gem, and this will be included in the name of the Grimoire once it drops as well as when it is in your inventory.
