Ground mud runes

 are a quest item used during the Eyes of Glouphrie quest by using a pestle and mortar on a Mud rune. Adding them to a bucket of sap turns it into magic sap which can be used as a glue to repair a broken machine in Brimstail's cave near the Gnome Stronghold.

Ground mud runes are also used to make Extreme magic potions, by using ground mud runes on a 3-dose Magic potion at level 91 Herblore, granting 250 Herblore experience.