'pharmaceutical grade clay' versus 'the natural and the commercial herbalist clay', and found an appreciable depletion of trace elements in the pharmaceutical grade clay. On the other hand, certain clays are typically heated or cooked before use. Medicinal clay is typically available in health food stores as a dry powder, or in jars in its liquid hydrated state – which is convenient for internal use. For external use, the clay may be added to the bath, or prepared in wet packs or poultices for application to specific parts of the body. Often, warm packs are prepared; the heat opens up the pores of the skin, and helps the interaction of the clay with the body. In the European health spas, the clay is prepared for use in a multitude of ways – depending on the traditions of a particular spa; typically it is mixed with peat and matured in special pools for a few months or even up to two years. "The majority of spas … use artificial ponds where the natural ("virgin") clay is mixed with mineral, thermo-mineral, or sea water that issues in the vicinity of the spas or inside the spa buildings." Trace minerals Clays contain large amounts of trace minerals. It is common to see as many as 75 different trace minerals in Montmorillonite clays. Specific trace minerals that various clays possess vary very widely. Also, the amount of any particular trace mineral in any specific clay varies a lot among clays from different locations. For example, the amount of iron in various bentonite clays can vary from 2.5 to 3%. Uses Skin conditions Many types of skin conditions have been treated by the application of medicinal clay. Montmorillonite has shown its effectiveness in this area. It has also been used as a base ingredient for tissue engineering. Clay is used in many dermatological over-the-counter remedies, such as in acne treatments (this information may not be mentioned on the label specifically). Internal use There are many over the counter remedies for internal use that contained clay before discontinuation. Examples include Kaopectate (Upjohn), Rheaban (Leeming Div., Pfizer), and Diar-Aid (Thompson Medical Co.). The labels on all of these showed the active ingredient to be Attapulgite, each tablet containing 600 (or 750 mg) of this component along with inert materials or adjuvants. However, since April 2003, attapulgite medication was discontinued due to lack of evidence according to the