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
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Date
2019-06-06
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Schweizerbart Science Publishers
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 A 2 B 3(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 F e 0.5 2 + Fe 0.5 3 + 2 Fe 3 3 + PO 4 3 OH 5 , that for frondelite is Mn 0.5 2 + Fe 0.5 3 + 2 Fe 3 3 + PO 4 3 OH 5 and that for plimerite is Z n 2 Fe 3 3 + P O 4 3 OH 4 ( H 2 O ) . 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 Fe 1.33 2 + Mn 0.52 2 + Zn 0.03 Ca 0.05 Fe 3.03 3 + Al 0.01 P 2.97 H 6.17 O 17 . The simplified formula is F e 2 + , M n 2 + 2 F e 3 3 + P O 4 3 OH 4 ( H 2 O ) . 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 [d meas/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. 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 A 2 B 3(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 F e 0.5 2 + Fe 0.5 3 + 2 Fe 3 3 + PO 4 3 OH 5 , that for frondelite is Mn 0.5 2 + Fe 0.5 3 + 2 Fe 3 3 + PO 4 3 OH 5 and that for plimerite is Z n 2 Fe 3 3 + P O 4 3 OH 4 ( H 2 O ) . 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 Fe 1.33 2 + Mn 0.52 2 + Zn 0.03 Ca 0.05 Fe 3.03 3 + Al 0.01 P 2.97 H 6.17 O 17 . The simplified formula is F e 2 + , M n 2 + 2 F e 3 3 + P O 4 3 OH 4 ( H 2 O ) . 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 [d meas/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. 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 A 2 B 3(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 F e 0.5 2 + Fe 0.5 3 + 2 Fe 3 3 + PO 4 3 OH 5 , that for frondelite is Mn 0.5 2 + Fe 0.5 3 + 2 Fe 3 3 + PO 4 3 OH 5 and that for plimerite is Z n 2 Fe 3 3 + P O 4 3 OH 4 ( H 2 O ) . 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 Fe 1.33 2 + Mn 0.52 2 + Zn 0.03 Ca 0.05 Fe 3.03 3 + Al 0.01 P 2.97 H 6.17 O 17 . The simplified formula is F e 2 + , M n 2 + 2 F e 3 3 + P O 4 3 OH 4 ( H 2 O ) . 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 [d meas/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. © 2018 E. Schweizerbart’sche Verlagsbuchhandlung
Description
Keywords
Minerals, X-ray diffraction, Neutron diffraction, Cations, Crystal structure, Iron phosphates
Citation
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(2), 389-397. doi:10.1127/ejm/2019/0031-2823