Investigation of manganese in salt- and freshwater pearls

The trace element distribution in natural and cultured pearls is analysed by micro-PIXE, cathodoluminescence (CL) microscopy and spectroscopy and electron spin resonance (ESR) spectroscopy to develop a new method to distinguish cultured from natural pearls. These different kinds of pearls can be identified by their manganese content and its distribution in aragonite and calcite structure, respectively, Manganese content of natural freshwater pearls from Persian Gulf was compared to that of natural freshwater pearls from the Mississippi river (USA). Moreover manganese content of tissue-graft freshwater pearls from Chansu. (China) was compared to that of natural freshwater pearls from the Mississippi river (USA). It was proved that the Chinese freshwater tissue-graft cultured pearls generally contain domains of calcite, emitting orange Mn2+-activated CL which are almost absent in the natural freshwater pearls from the Mississippi river. Freshwater pearls showing much higher Mn concentrations build in calcitic and aragonitic parts compared to saltwater pearls. (C) 2001 Elsevier Science BN. All rights reserved.