Vivianite on Weichselian mammalian bones from Orvelte (Drenthe, The Netherlands)

In trenches dug for a gas main near Orvelte in the province of Drenthe (The Netherlands), an in situ occurrence of fossil mammalian bones was noted in the spring of 1991. In view of the importance of this find, it was soon decided to carry out a large-scale excavation at the site. The collected bones were covered in blue crusts, which at first sight were identified as vivianite, an assignment that was subsequently confirmed. This Fe-phosphate is a common mineral in the Drenthe peat districts. Since the geology of the site was studied in detail, and this vivianite occurrence included euhedric crystals, a description of this find seemed warranted. The results of mineralogical analyses are presented, and previous vivianite records from Drenthe are briefly discussed. The crystal morphology of the Orvelte vivianite is described, and data obtained through X-ray diffraction analysis, X-ray fluorescence spectroscopy and scanning electron microscopy are presented. X-ray diffraction analysis shows that in addition to the monoclinic phase an admixture of an oxidised phase characterises this vivianite record; this observation corresponds with previous records by various authors.