By the early 1970’s the need for sources of homogeneous clay samples had become apparent to researchers. Natural deposits are so variable that data generated by different investigators working at the same outcrop often cannot be compared with confidence. Thus the Clay Minerals Society set up the Source Clays Project.
The Society’s Source Clays Repository offers two series of materials, the Source Clays and the Special Clays.
The Source Clays are derived from large, reasonably homogenized stocks. Thus, over the years, data on these reference materials can be compared. The samples have been carefully selected from the source deposits by professionals to minimize in situ variations. Because any beneficiation technique can bring about changes in properties, pre-treatment usually involves only low-temperature, steam-fired tray drying, and imp or Raymond mill pulverization. Each original sample consisted of one metric ton.
The Special Clays are rare but of great theoretical interest. No attempt has been made to homogenize or beneficiate them.