Rubium has high reactivity with water. Thus, during the quest, it is used on the steamers to raise the room temperature significantly in order to disrupt the workers. However, the rubium will burn up if players get kicked out, so they still need to be careful not to get caught. After the quest, players may sell rubium to Ezekial Lovecraft in his fishing shop, based in Witchaven for 10 coins per ore. Doing this is required for the medium Ardougne task 'Volatile Valuables'. During Salt in the Wound, Ezekial utilises homemade rubium grenades as his primary weapon.
Rubium may be based on the real-life metallic element rubidium, which is also highly reactive with water and chemically unstable. Although rubidium is a silvery-white Group I alkali metal, it burns with a reddish-violet colour in a flame. In contrast, rubium is directly coloured as red. However, its reactivity is a closer match to Sodium.
Despite its high reactivity with water, using it on any water source (sink, well, etc.) or any container of water (bowl of water, bucket of water, etc.) only yields this message: "Nothing interesting happens."