TY - JOUR
T1 - Ferrobobfergusonite, ana2fe2+5fe3+al(po4)6, a new mineral of the bobfergusonite group from the victory mine, custer county, south dakota, usa
AU - YANG, HEXIONG
AU - YONG, TOMMY
AU - DOWNS, ROBERT T.
N1 - Publisher Copyright:
© 2021 Mineralogical Association of Canada. All rights reserved.
PY - 2021
Y1 - 2021
N2 - A new mineral species, ferrobobfergusonite, ideally ANa2Fe2+5Fe3+Al(PO4)6, has been found in the Victory Mine, Custer County, South Dakota, USA. It is massive and associated with ferrowyllieite, schorl, fillowite, arrojadite, quartz, and muscovite. Broken pieces of ferrobobfergusonite are blocky or tabular with single crystals up to 0.9 3 0.7 3 0.4 mm. No twinning or parting is observed macroscopically. The mineral is deep green-brown and transparent with a pale green-yellow streak and vitreous luster. It is brittle and has a Mohs hardness of ∼5, with perfect cleavage on {010}. The measured and calculated densities are 3.68(1) and 3.69 g/cm3, respectively. Optically, ferrobobfergusonite is biaxial (+), with a=1.698 (2), b =1.705 (2), c=1.727 (2) (white light), 2V (meas.)=65(2)8, 2V (calc.)=608, with orientation of the optic axes a _ X=168, b= Y, with X = yellowish brown, Y = brown, and Z = deep brown. The dispersion is very strong with r . v. The calculated compatibility index based on the empirical formula is 0.017 (superior). An electron microprobe analysis yielded an empirical formula (based on 24 O apfu) of (Na1.72A1.28)R3.00(Fe2+3.50Mn0.89Mg0.44Ca0.13)R4.96(Fe3+0.77Al0.23)R1.00Al(PO4)6. Ferrobobfergusonite is isostructural with bobfergusonite, a member of the alluaudite supergroup. It is monoclinic, with space group P21/n and unit-cell parameters a = 12.7156(3), b = 12.3808(3), c = 10.9347(3) A, b = 97.3320(10)8, and V = 1707.37(7) A3. The crystal structure of ferrobobfergusonite contains six octahedral M (= Fe2+, Mg, Mn2+, Al, Fe3+) sites and five X (=Na, Mn2+, Ca) sites with coordination numbers between 6 and 8. The six MO6 octahedra share edges to form two types of kinked chains extending along [101], with one consisting of M1-M4-M5 linkages and the other of M2-M3-M6 linkages. These chains are joined by PO4 tetrahedra to form sheets parallel to (010), which are linked together through corner-sharing between PO4 tetrahedra and MO6 octahedra in the adjacent sheets, leaving open channels parallel to a, where the large X cations are situated. The M cations are strongly ordered over the six sites, with M1, M2, M3, and M4 being dominantly occupied by Fe2+, and M5 and M6 by Fe3+and Al, respectively. Among the five X sites, the X1 site is filled with Mn2+ and Ca, whereas the X2-X5 sites are partially occupied by Na.
AB - A new mineral species, ferrobobfergusonite, ideally ANa2Fe2+5Fe3+Al(PO4)6, has been found in the Victory Mine, Custer County, South Dakota, USA. It is massive and associated with ferrowyllieite, schorl, fillowite, arrojadite, quartz, and muscovite. Broken pieces of ferrobobfergusonite are blocky or tabular with single crystals up to 0.9 3 0.7 3 0.4 mm. No twinning or parting is observed macroscopically. The mineral is deep green-brown and transparent with a pale green-yellow streak and vitreous luster. It is brittle and has a Mohs hardness of ∼5, with perfect cleavage on {010}. The measured and calculated densities are 3.68(1) and 3.69 g/cm3, respectively. Optically, ferrobobfergusonite is biaxial (+), with a=1.698 (2), b =1.705 (2), c=1.727 (2) (white light), 2V (meas.)=65(2)8, 2V (calc.)=608, with orientation of the optic axes a _ X=168, b= Y, with X = yellowish brown, Y = brown, and Z = deep brown. The dispersion is very strong with r . v. The calculated compatibility index based on the empirical formula is 0.017 (superior). An electron microprobe analysis yielded an empirical formula (based on 24 O apfu) of (Na1.72A1.28)R3.00(Fe2+3.50Mn0.89Mg0.44Ca0.13)R4.96(Fe3+0.77Al0.23)R1.00Al(PO4)6. Ferrobobfergusonite is isostructural with bobfergusonite, a member of the alluaudite supergroup. It is monoclinic, with space group P21/n and unit-cell parameters a = 12.7156(3), b = 12.3808(3), c = 10.9347(3) A, b = 97.3320(10)8, and V = 1707.37(7) A3. The crystal structure of ferrobobfergusonite contains six octahedral M (= Fe2+, Mg, Mn2+, Al, Fe3+) sites and five X (=Na, Mn2+, Ca) sites with coordination numbers between 6 and 8. The six MO6 octahedra share edges to form two types of kinked chains extending along [101], with one consisting of M1-M4-M5 linkages and the other of M2-M3-M6 linkages. These chains are joined by PO4 tetrahedra to form sheets parallel to (010), which are linked together through corner-sharing between PO4 tetrahedra and MO6 octahedra in the adjacent sheets, leaving open channels parallel to a, where the large X cations are situated. The M cations are strongly ordered over the six sites, with M1, M2, M3, and M4 being dominantly occupied by Fe2+, and M5 and M6 by Fe3+and Al, respectively. Among the five X sites, the X1 site is filled with Mn2+ and Ca, whereas the X2-X5 sites are partially occupied by Na.
KW - Alluaudite
KW - Crystal structure
KW - Ferrobobfergusonite
KW - Raman spectra
KW - Wyllieite
KW - X-ray diffraction
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U2 - 10.3749/CANMIN.2000064
DO - 10.3749/CANMIN.2000064
M3 - Article
AN - SCOPUS:85114737226
VL - 59
SP - 617
EP - 627
JO - Canadian Mineralogist
JF - Canadian Mineralogist
SN - 0008-4476
IS - 3
ER -