Uncut onyx is the final tier of gems that players can get. This gem used to be exclusive to the Castle Wars Mini-game, but was later added as drop-able items from the Tzhaar monsters. This item is used to make the Amulet of fury, and Ring of stone. It can also be obtained by completing the Fight Kiln Mini-game and selecting the uncut onyx as a reward, it can also be obtained from the Tzhaar shop for 2,700,000 Tokkul. Most users seem to just kill npc's to get onyx's other than wasting a lot of time just to receive one per mini game as a reward. You can also cut an uncut onyx to get a cut onyx and cut it once more to obtain onyx bolt tips. This, however, is not recommended as Corporeal Beast drops Onyx Bolts.
Due to the low value of the Amulet of Fury in Soulsplit, the value of an uncut onyx is significantly lower than what it should be, this means very few, if any uncut onyx's are seen in-game due to a lack of people wanting to buy them over stronger and more expensive gear.