Unicorn horn dust
Unicorn horn dust can be created by using a Pestle and mortar on an Unicorn horn. You can obtain an Unicorn horn as a drop from Unicorns and you can buy a Pestle and mortar for 3 coins in any General store. The unicorn horn dust is only used to make antipoisons and super antipoisons by using the Herblore skill.
Antipoisons are created by using unicorn horn dust on an Unfinished marrentill potion. This requires a herblore level of 8 and will grant 190 experience.
Super antipoisons are created by using unicorn horn dust on an Unfinished irit potion. This requires a herblore level of 52 and will grant 530 experience.