The use of x-ray diffraction for the identification of the clay mineral composition of ceramic paste is complicated by the fact that the kiln firing of the ceramic to temperatures in excess of 500°C results in the clay minerals being altered. The procedure described involves heating crushed ceramic fragments to temperatures which are high enough to cause recrystallization. The minerals which are formed are then identified by x-ray diffraction and from this information conclusions can be drawn concerning the original clay mineral composition. Examples are shown for the clay minerals kaolinite, montmorillonite and palygorskite -- AATA