Grahampearsonite, Ca2P2O7, a new mineral found in a super-deep diamond from Juína, Brazil

Abstract

Grahampearsonite, ideally Ca2P2O7, is a new mineral (IMA 2025-017) that was found in a multiphase inclusion in a super-deep diamond (sample RV43) from the Chapadão plateau, Mato Grosso, Brazil. The new mineral is closely associated with tuite and with other mineral inclusions in the host diamond (that are not in direct contact with grahampearsonite) including larnite, merrillite, apatite, diopside, ilmenite, magnetite, calcite, and an unidentified phosphate phase. X-ray diffraction analyses, performed directly on the inclusion while still entrapped in the diamond, revealed a tetragonal crystal structure (space group P41), with unit-cell parameters a = 6.6966(16) Å, c = 24.145(11) Å, and V = 1082.8(6) Å3. The identification of grahampearsonite as the natural analog of synthetic β-Ca2P2O7 is strongly supported by micro-Raman, FTIR, crystal chemical, and X-ray diffraction data. The occurrence of grahampearsonite and tuite in a super-deep diamond indicates that grahampearsonite could be related to the decomposition of tuite and may provide new insights into the Earth's deep phosphorus reservoir and the crust-mantle phosphorus cycle. The new mineral honors Graham D. Pearson, University of Alberta, for his outstanding contributions to diamond research.