A multi-domain gem-grade Brazilian apatite

作者：Baikie Tom^*; Schreyer Martin K; Wong Chui Ling; Pramana Stevin S; Klooster Wim T; Ferraris Cristiano; McIntyre Garry J; White T J

来源：American Mineralogist, 2012, 97(10): 1574-1581.

DOI：10.2138/am.2012.4069

• Apatite
• X-ray diffraction
• Laue neutron diffraction
• synchrotron X-ray diffraction

A gem-grade apatite from Brazil of general composition (Ca,Na)(10)[(P,Si,S)O-4](6)(F,Cl,OH)(2) has been studied using single-crystal X-ray and neutron diffraction together with synchrotron powder X-ray diffraction. Earlier electron microscopy studies had shown the nominally single-phase apatite contains an abundant fluorapatite (F-Ap) host, together with chloro-hydroxylapatites (Cl/OH-Ap) guest phases that encapsulate hydroxylellestadite (OH-El) nanocrystals. While the latter features appear as small (200-400 nm) chemically distinct regions by transmission electron microscopy, and can be identified as separate phases by synchrotron powder X-ray diffraction, these could not be detected by single-crystal X-ray and neutron analysis. The observations using neutron, X-ray and electron probes are however consistent and complementary. After refinement in the space group P6(3)/m the tunnel anions F- are fixed at z = 1/4 along %26lt; 001 %26gt;, while the anions Cl- and OH- are disordered, with the suggestion that O-H center dot center dot center dot O-H center dot center dot center dot hydrogen-bonded chains form in localized regions, such that no net poling results. The major cations are located in the 4f/A(F)O(6) metaprism (Ca+Na), 6h A(T)O(6)X tunnel site (Ca only), and 6h BO4 tetrahedron (P+Si+S). The structural intricacy of this gem stone provides further evidence that apatite microstructures display a nano-phase separation that is generally unrecognized, with the implication that such complexity may impact upon the functionality of technological analogues.

• 出版日期2012-10
• 单位南阳理工学院