The most commonly-found clay, bentonite clay comes from volcanic ash. This clay swells when you mix it with water, making it expand. The expansion causes its molecules to get charged. That electricity then helps the clay pull out toxins from the pores, and cling to the clay magnetically. Bentonite clay, hence, is great for deep pore cleansing. So, if you have very oily, blackhead prone-skin that is always breaking out, opt for this. If you have sensitive skin, stay away from this, as it contains lead, and can be harsh.