The calcioferrite group has been formally approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (proposal 19-B). It comprises four minerals with C-centred monoclinic cells and general formula Ca4A2+B3+4(PO4)6(OH)4·12H2O, where A and B = Mg and Fe for calcioferrite, Mg and Al for montgomeryite, Mn and Fe for zodacite and Mn and Al for fanfaniite, together with the triclinic mineral kingsmountite, Ca3Mn2+Fe2+Al4(PO4)6(OH)4·12H2O. The minerals with B = Fe form the calcioferrite subgroup and those with B = Al form the montgomeryite subgroup.

The triclinic member was recently approved as the mineral “aniyunwiyaite” (IMA2018-054). New measurements on the holotype specimen of kingsmountite, however, show that it has the same crystallographic and chemical properties as “aniyunwiyaite” and, consequently, “aniyunwiyaite” has been discredited as being kingsmountite. Kingsmountite is triclinic, P−1, with a = 20.067(6) Å, b = 13.197(4) Å, c = 6.255(3) Å, α = 89.35(2)°, β = 91.21(2)°, γ = 112.20(2)°, V = 1533.4(10) Å3 and Z = 2. The structure was solved and refined to Robs = 0.059 for 4351 reflections with I > 3σ(I). The crystal structure is a superstructure of the C-centred monoclinic montgomeryite structure, having a doubled am cell parameter. The superstructure results from ordering of octahedrally coordinated Mn in one of four independent 8-coordinated Ca sites, and ordering of A site cations, which in the Ca4AB4(PO4)6(OH)4·12H2O minerals are statistically distributed over half-occupied sites.

You do not currently have access to this article.