ToME WikiOrvin: Quicksand looks like mud, but when you enter it, your speed is reduced and you receive a message indicating that you have sunk into quicksand. The extent of speed reduction depends on your weight, with greater weight causing greater speed reduction due to greater sinking. Quicksand does not affect you if you are levitating/flying.
Quicksand can be changed by fire into sand, and sand can be changed by water into quicksand.