Baseline Studies of the Clay Minerals Society Source Clays: Geological Origin

In any clay deposit, the nature of the mineral assemblage and the composition of individual clay minerals can change radically in a few em. Consequently, any given locality can contain many subtly different types of clay minerals. Results from different laboratories on ostensibly the same clay material may not always be comparable because the samples may indeed not contain an assembly of identical clay minerals. Such confusion slows the understanding of this important group of minerals. Several attempts were made to provide investigators with reasonably constant clay materials, the first being that of the American Petroleum Institute Project 49 (Kerr, 1949). The Clay Minerals Society Source Clays project proposed to provide investigators with gently homogenized clay materials, carefully collected and processed under the supervision of clay specialists. The collection would include metric ton amounts to ensure a long-lasting collection. The program began in 1972, with the introduction of the materials described in this paper. Later the program expanded to include the Special Clays. These samples are materials not amenable to homogenization, or they are available in very small amounts.