IMA 2018-004 = ferrorockbridgeite and the rockbridgeite group

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Marco E. Ciriotti
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IMA 2018-004 = ferrorockbridgeite and the rockbridgeite group

Messaggio da Marco E. Ciriotti » lun 17 dic, 2018 11:52

Prossima pubblicazione.

Referenza:
▪ Grey, I.E., Kampf, A.R., Keck, E., Cashion, J.D., MacRae, C.M., Gozukara, Y., Peterson, V.K., Shanks, F.L. (2019): The rockbridgeite group approved and a new member, ferrorockbridgeite, (Fe2+,Mn2+)2(Fe3+)3(PO4)3(OH)4(H2O), described from the Hagendorf Süd pegmatite, Oberpfalz, Bavaria. European Journal of Mineralogy, 31, (in press).
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 25909
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Re: IMA 2018-004 = ferrorockbridgeite and the rockbridgeite group

Messaggio da Marco E. Ciriotti » mer 22 mag, 2019 10:25

Pubblicazione effettuata.

Referenza:
▪ Grey, I.E., Kampf, A.R., Keck, E., Cashion, J.D., MacRae, C.M., Gozukara, Y., Peterson, V.K., Shanks, F.L. (2019): The rockbridgeite group approved and a new member, ferrorockbridgeite, (Fe2+,Mn2+)2(Fe3+)3(PO4)3(OH)4(H2O), described from the Hagendorf Süd pegmatite, Oberpfalz, Bavaria. European Journal of Mineralogy, 31, 389-397.

Abstract:
The rockbridgeite group has been officially established by the IMA Commission on New Minerals, Nomenclature and Classification. The general formula is based on the structure and is A2B3(PO4)3(OH, H2O)5, where A = the octahedrally coordinated M2 site, in which divalent cations are ordered, and B = the octahedrally coordinated M1 + M3 sites, which contain predominantly Fe3+, with trace Al. The different rockbridgeite-group minerals are distinguished by the occupancy of the A site. The ideal formula for rockbridgeite is (Fe2+0.5Fe3+0.5)2Fe3+3(PO4)3(OH)5⁠, that for frondelite is (Mn2+0.5Fe3+0.5)2Fe3+3(PO4)3(OH)5 and that for plimerite is Zn2Fe3+3(PO4)3(OH)4(H2O)⁠. In order to preserve the identity of frondelite and rockbridgeite within the structure-based formalism, these species correspond to mid-series compositions. We describe here the new end-member, ferrorockbridgeite, with dominant Fe2+ in the A site, from the Hagendorf Süd pegmatite mine, Oberpfalz, Bavaria. Electron microprobe analyses, coupled with Mössbauer spectroscopy, gives the empirical formula Fe2+1.33Mn2+0.52Zn0.03Ca0.05Fe3+3.03Al0.01P2.97H6.17O17⁠. The simplified formula is (Fe2+,Mn2+)2Fe3+3(PO4)3(OH)4(H2O)⁠. Ferrorockbridgeite is orthorhombic, space group Bbmm, with a = 13.9880(4), b = 16.9026(5), c = 5.1816(1) Å, V = 1225.1 Å3 and Z = 4. The six strongest lines in the X-ray powder diffraction pattern are [dmeas/Å (I) (hkl)]: 4.853 (26) (101), 3.615 (24) (240), 3.465 (33) (301), 3.424 (39) (410), 3.205 (100) (321) and 1.603 (24) (642). Optically, ferrorockbridgeite is biaxial (–) with α = 1.763(3), β = 1.781(calc), γ = 1.797(3) (white light) and 2V (meas.) = 87(1)° from extinction data. The optical orientation is X = c, Y = a, Z = b. The pleochroism is X = blue green, Y = olive green, Z = yellow brown; X ≈ Y > Z.
Marco E. Ciriotti

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