research papers Acta Crystallographica Section B Structural Crystal chemistry of mimetite, Science Pb10(AsO4)6Cl1.48O0.26, and finnemanite, ISSN 0108-7681 Pb10(AsO3)6Cl2 Tom Baikie,a* Cristiano The crystal chemistries of synthetic mimetite, Received 22 October 2007 a,b a,c 5+ Accepted 11 December 2007 Ferraris, Wim T. Klooster, Pb10(As O4)6(Cl2 À xOx/2), a neutral apatite, and finnemanite, a a 3+ S. Madhavi, Stevin S. Pramana, Pb10(As O3)6Cl2, a reduced apatite, were characterized using Allan Pring,d G. Schmidtd and a combination of X-ray powder diffraction, neutron diffrac- T. J. Whitea tion, transmission electron microscopy and X-ray photoelec- tron spectroscopy. Both phases conform to hexagonal P63/m symmetry; however, the temperature-driven transformation of a School of Materials Science and Engineering, clinomimetite to mimetite described earlier was not Nanyang Technological University, Block N4.1, confirmed. The average mimetite structure is best described 50 Nanyang Avenue, Singapore 639798, bLaboratoire de Mine´ralogie, USM 201, through the introduction of partially occupied oxygen sites. A Muse´um National d’Histoire Naturelle, CP 52, better understanding of the mixed arsenic speciation in 61 Rue Buffon, 75005 Paris, France, cInstitute of apatites can guide the formulation of waste form ceramics Materials Research and Engineering, 3 Research and improve models of long-term durability after landfill d Link, Singapore 117602, and Department of disposal. Mineralogy, South Australian Museum, North Terrace, Adelaide, Australia Correspondence e-mail:
[email protected] 1. Introduction Anthropogenic releases of lead and arsenic oxides from mineral resources present a health risk to surrounding popu- lations and the environment.