Onyx bolt tips are attached to the tips of rune bolts, and can then be enchanted. Once onyx bolt tips have been attached, the rune bolts become onyx bolts.
Onyx bolt tips can be created through the Fletching skill. A player must have a Fletching level of 73 and take a cut onyx and use a chisel with it to make 24 Onyx bolt tips. This is not recommended because the gem itself is worth far more than the bolt tips. Instead, it's recommended to buy the already cut Onyx bolt tips from the TzHaar.
Attaching onyx bolt tips also requires a Fletching level of 73, and for each onyx bolt tip attached to a rune bolt, a player is granted 9.4 Fletching experience.
Onyx bolt tips are obtainable from killing Tzhaar citizens at a "rare" rate. However, a player may collect the Tokkul and use them to buy the onyx bolt tips themselves. 1 onyx bolt tip is worth 13,500 Tokkul.