Rhassoul has been mined in the Atlas for centuries, and almost every mistake people make with it comes from treating it like a face wash. It is a mineral clay: it binds to oil and lifts it away, and it will keep going long after it has taken what you wanted it to take.
Mix it with warm water, not hot. Leave it on until it is tacky, not cracked — cracked means it has started pulling water out of the skin instead of oil. Five minutes is usually enough.