The compound responsible for the blue colour in Maya blue has not been identified. It is not known whether it be organic or inorganic in nature. Although the clay mineral attapulgite was identified as the main constitutent, this is not a coloured material. only manganese and iron were found in very small traces. At the time of the publication (1962) analytical tools were not sufficiently sensitive to allow determination of very low concentrations of organic compounds. The different properties of clays and the possible way in which an organic component might be combined are considered. the small size of the available specimens is a handicap and knowledge of the pigment's distribution still incomplete although the Yucatan Peninsula was one centre of production. Unfortunately attapulgite had not been found there among the clay samples analysed, although this does not rule out its presence. The problem of Maya blue illustrates some of the problems which may be encountered when trying to identify archaeological material. References. -- ICCROM