IMA 2023-028 = regerite

[Marco E. Ciriotti]

Referenza:
▪ Rewitzer, C., Hochleitner, R., Grey, I.E., Kampf, A.R., Boer, S., MacRae, C.M. (2023): Regerite, KFe6(PO4)4(OH)7(H2O)6⋅4H2O, the first new mineral species from the Kreuzberg pegmatite, Pleystein, Oberpfalz, Bavaria, Germany. European Journal of Mineralogy, 35, 805-812.

Abstract:
Regerite, KFe6(PO4)4(OH)7(H2O)6·4H2O, is the first new mineral species to be characterised from the Kreuzberg pegmatite, Pleystein, in the Oberpfalz, Bavaria. It was found in vugs on a specimen of drusy quartz, associated with rockbridgeite, strengite and phosphosiderite. Regerite occurs as clusters of yellowish-green prisms, typically 5 to 20 µm wide and up to 0.1 mm long. The crystals are flattened on {100} and elongated along [001], and they display the forms {100}, {010} and {011}. The measured density is 2.69(2) g cm−3. Optically, regerite crystals are biaxial (+), with α = 1.670(5), β = 1.690(5) and γ = 1.730(5) (measured in white light), and 2V (meas) is 76(2)◦. The empirical formula from electron microprobe analyses and crystal structure refinement is K0.95(Fe3+5.66Ti0.45)66.11(PO4)3.95(OH)7[(H2O)5.33(OH)0.88]66.21·4H2O. Regerite has monoclinic symmetry, with space group P21/c and unit-cell parameters a = 15.408(11) Å, b = 17.311(11) Å, c = 9.870(11) Å, β = 95.42(2)◦, V = 2621(3) Å3 and Z = 4. The crystal structure was refined using synchrotron single-crystal data to wRobs = 0.065 for 6088 reflections with I > 3σ (I ). The structure type has not been previously reported. It is made of heteropolyhedral layers parallel to {100} that consist of Fe-centred octahedra and PO4 tetrahedra. The layers are interconnected via edge-shared octahedral dimers to form slit-like channels along [001] that are occupied by K+ ions and water molecules.

NdR: KFe3+6(PO4)4(OH)7(H2O)6·4H2O. Empirical formula K0.95(Fe3+5.66Ti4+0.45)66.11(PO4)3.95(OH)7[(H2O)5.33(OH)0.88]66.21·4H2O.