Heat induced transformation of fossil mastodon ivory into turquoise 'odontolite'. Structural and elemental characterisation

The present work deals with the structural and elemental analysis of turquo ise mineral imitations as 'odontolite' or bone turquoise by transmission el ectron microscopy (TEM), scanning electron microscopy (SEM-EDX) and particl e induced X-ray and gamma -ray emission (PIXE-PIGE). The aim of the work is to evidence the former deliberate transformation of fossilised ivory by ma n in order to transform them into semi-precious stones. We show that the cr ystal structure of 'odontolite' artefacts consisting of fluorapatite (Ca-5( PO4)(3)F) corresponds to that of heated fossil mastodon ivory (12-15 millio n years old). Metallic traces detected by PIXE-PIGE in these 'odontolites' are discussed in order to explain their rule for coloration. Other more gre enish turquoise imitations have a bone-like structure and composition, and carbonate-hydroxylapatite. The presence of copper salts at the surface is r esponsible for their green coloration. (C) 2000 Editions scientifiques et m edicales Elsevier SAS. All rights reserved.