Mesopotamian seals and duckweights of the period 2000 - 1600 BC are often made of iron-stone which is usually refered to as 'heamatite'. In two prevoius experiments we have shown that these objects contain different types of oxides. We propose to enlarge our data baseand indepth knowledge of the mineral composition of the Mesopotamian 'heamatite' seals and duck-weights by studying the objects from the RMO-Leiden collection. Especially, their duckweight collection will allow us further insight into the material used for the production of these objects.