TY - JOUR
T1 - The crystal structure of vladimirite, with a revised chemical formula, Ca4(AsO4)2(AsO3OH)·4H 2O
AU - Yang, Hexiong
AU - Evans, Stanley H.
AU - Downs, Robert T.
AU - Jenkins, Robert A.
PY - 2011/8
Y1 - 2011/8
N2 - Two samples of vladimirite, one from Bou Azzer, Morocco, and the other from a new occurrence in Copiapó, Chile (designated as R100075 and R080001, respectively), were examined with an electron microprobe, single-crystal X-ray diffraction, and Raman spectroscopy. Our results show that vladimirite is monoclinic with space group P21/c and unit-cell parameters a 5.8279(2), b 10.1802(4), c 22.8944(10) Å, β 96.943(2)°, and V 1348.35(9) Å3 for R100075 and a 5.8220(1), b 10.1750(2), c 22.8816(6) Å, β 96.902(1)°, and V 1345.66(5) Å3 for R080001. The structure determinations, with R1, = 0.022 and 0.023 for R100075 and R080001, respectively, yielded an ideal chemical formula Ca4(AsO4)2(AsO3OH)·4H 2O (Z = 4) for this mineral, in contrast to Ca5(AsO 4)2(AsO3OH)2·5H2O (Z = 3) documented in the literature. The chemical compositions for R100075 and R080001 are Ca4.03(AsO4)2(As 0.99O3OH)·4H2O and Ca 3.97(AsO4)2(As1.01O 3OH)·4H2O, with trace Zn and Mn, respectively. The structure is characterized by undulating layers formed by the four nonequivalent, rather irregular Ca polyhedra [CalO6(H2O), Ca2O6(H2O), Ca3O4(H 2O)3, and Ca4O5(H2O)3] linked through the sharing of edges and vertices. These undulating layers are parallel to (010) and are interconnected by AsO4 and ASO 3OH tetrahedra, as well as hydrogen bonds, along the b axis. Vladimirite is remarkable inasmuch as one of the hydrogen-bonded O-H···O distances (012H-H···O3) is only 2.465(2) Å, which is the shortest donoracceptor distance of all known Ca-bearing arsenate minerals, similar to the short donor-acceptor distances observed in several synthetic compounds containing AsO3OH groups.
AB - Two samples of vladimirite, one from Bou Azzer, Morocco, and the other from a new occurrence in Copiapó, Chile (designated as R100075 and R080001, respectively), were examined with an electron microprobe, single-crystal X-ray diffraction, and Raman spectroscopy. Our results show that vladimirite is monoclinic with space group P21/c and unit-cell parameters a 5.8279(2), b 10.1802(4), c 22.8944(10) Å, β 96.943(2)°, and V 1348.35(9) Å3 for R100075 and a 5.8220(1), b 10.1750(2), c 22.8816(6) Å, β 96.902(1)°, and V 1345.66(5) Å3 for R080001. The structure determinations, with R1, = 0.022 and 0.023 for R100075 and R080001, respectively, yielded an ideal chemical formula Ca4(AsO4)2(AsO3OH)·4H 2O (Z = 4) for this mineral, in contrast to Ca5(AsO 4)2(AsO3OH)2·5H2O (Z = 3) documented in the literature. The chemical compositions for R100075 and R080001 are Ca4.03(AsO4)2(As 0.99O3OH)·4H2O and Ca 3.97(AsO4)2(As1.01O 3OH)·4H2O, with trace Zn and Mn, respectively. The structure is characterized by undulating layers formed by the four nonequivalent, rather irregular Ca polyhedra [CalO6(H2O), Ca2O6(H2O), Ca3O4(H 2O)3, and Ca4O5(H2O)3] linked through the sharing of edges and vertices. These undulating layers are parallel to (010) and are interconnected by AsO4 and ASO 3OH tetrahedra, as well as hydrogen bonds, along the b axis. Vladimirite is remarkable inasmuch as one of the hydrogen-bonded O-H···O distances (012H-H···O3) is only 2.465(2) Å, which is the shortest donoracceptor distance of all known Ca-bearing arsenate minerals, similar to the short donor-acceptor distances observed in several synthetic compounds containing AsO3OH groups.
KW - Arsenate
KW - Crystal structure
KW - Raman spectra
KW - Vladimirite
KW - X-ray diffraction
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U2 - 10.3749/canmin.49.4.1055
DO - 10.3749/canmin.49.4.1055
M3 - Article
AN - SCOPUS:81355133499
VL - 49
SP - 1055
EP - 1064
JO - Canadian Mineralogist
JF - Canadian Mineralogist
SN - 0008-4476
IS - 4
ER -