A comparison of the Ca3(PO4)2 and CaSiO3 systems, with a new structure refinement of tuite synthesized at 15 GPa and 1300 °c

Richard M. Thompson, Xiande Xie, Shuangmeng Zhai, Robert T. Downs, Hexiong Yang

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


Tuite, the high-pressure γ-form of the Ca3(PO 4)2 system, has been synthesized from chlorapatite at 15 GPa and 1300 °C using a multi-anvil apparatus. Its crystal structure was determined with single-crystal X ray diffraction. It is isostructural with palmierite, with space group R3̄m and unit-cell parameters a = 5.2522(9) and c = 18.690(3) Å. The structure of tuite is characterized by three distinct polyhedra, PO4, Ca1O12, and Ca2O10, that are translationally interconnected in the sequence of PO 4-Ca2O10-Ca1O12-Ca2O10-PO4 along the c axis. Comparison of the CaSiO3 and Ca3(PO 4)2 polymorphic systems shows a striking resemblance in the evolution of atomic packing arrangements as the polymorphic density increases. In both cases, the Ca atoms are progressively incorporated into the (Ca+O) close-packed monolayers, consistent with the hypothesis that close packing is a consequence of volume decrease as density increases. Based on this observation, we predict a possible high-pressure post-tuite phase.

Original languageEnglish (US)
Pages (from-to)1585-1592
Number of pages8
JournalAmerican Mineralogist
Issue number8-9
StatePublished - 2013


  • Close-packing
  • Perovskite
  • Pseudowollastonite
  • Tuite
  • Whitlockite
  • Wollastonite

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology


Dive into the research topics of 'A comparison of the Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> and CaSiO<sub>3</sub> systems, with a new structure refinement of tuite synthesized at 15 GPa and 1300 °c'. Together they form a unique fingerprint.

Cite this