The rhassoul or ghassoul is a natural mineral clay mined in the Atlas Mountains of Morocco since the eighth century. It is combined with water to clean the body and has been used by Moroccan women for centuries to care for their skin and hair. Rhassoul contains silica, iron, magnesium, potassium, sodium, lithium, and trace elements.
Today, rhassoul is used in Turkish baths. Along with a glove, or "kessa", Rhassoul is used as a facial mask and poultice to the body. It is similar to a western style mud wrap. It is intended to soften the skin, reduce sebum secretion, regenerate the skin by removing dead cells, and rebalance the skin by tightening the pores. 
Rhassoul clay is also used for hair washing. It is a suggested substitution for shampoo. Moreover rhassoul is useful for dandruff prevention and head skin nurturance. It is recommend to be used with natural oils or use oils after washing your head because the clay has 
- The Complete Idiot's Guide to Making Natural Beauty Products by Sally W. Trew, Zonella B. Gould
- Handbook of Medical Tourism Development by María Todd, p. 202 
- Ask Question Online - Rhassoul clay for hair washing