Promethium rock is a mining rock used in the Dungeoneering skill, requiring 90 Mining to mine and will always contain 5 ores. However, the player can crush up to 4 out of 5 of these ores whilst extracting them from the rock. This means that each rock can give between 1-5 Promethium ores before it is depleted and unlike rocks on Gielinor it would not respawn. With a gatherer ring, it is possible to mine up to 10 ores.

The player is given a message when they have successfully mined an ore or if they have crushed it; however, these messages can be hidden by the game filter. It is a Tier 10 rock and provides the highest quality ore that can be mined in the Dungeoneering skill. A Complexity level of 3 or higher is required to find this rock whilst Dungeoneering.

In Thok It To 'Em, the promethium ore is called Crumbly stuff by Thok, and has an examine of This where Marm gets crumbly from.