| Reference Type | Journal (article/letter/editorial) |
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| Title | Crystal structure determination of karibibite, an Fe3+ arsenite, using electron diffraction tomography |
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| Journal | Mineralogical Magazine |
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| Authors | Colombo, Fernando | Author |
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| Mugnaioli, Enrico | Author |
| Vallcorba, Oriol | Author |
| García, Alberto | Author |
| Goñi, Alejandro R. | Author |
| Rius, Jordi | Author |
| Year | 2017 (October) | Volume | 81 |
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| Issue | 5 |
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| Publisher | Mineralogical Society |
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| DOI | doi:10.1180/minmag.2016.080.159Search in ResearchGate |
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| Generate Citation Formats |
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| Classification | Not set | LoC | Not set |
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| Mindat Ref. ID | 244940 | Long-form Identifier | mindat:1:5:244940:5 |
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| GUID | 0 |
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| Full Reference | Colombo, Fernando, Mugnaioli, Enrico, Vallcorba, Oriol, García, Alberto, Goñi, Alejandro R., Rius, Jordi (2017) Crystal structure determination of karibibite, an Fe3+ arsenite, using electron diffraction tomography. Mineralogical Magazine, 81 (5) 1191-1202 doi:10.1180/minmag.2016.080.159 |
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| Plain Text | Colombo, Fernando, Mugnaioli, Enrico, Vallcorba, Oriol, García, Alberto, Goñi, Alejandro R., Rius, Jordi (2017) Crystal structure determination of karibibite, an Fe3+ arsenite, using electron diffraction tomography. Mineralogical Magazine, 81 (5) 1191-1202 doi:10.1180/minmag.2016.080.159 |
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| Abstract/Notes | The crystal structure of karibibite, Fe33+(As3+O2)4(As23+O5)(OH), from the Urucum mine (Minas Gerais, Brazil), was solved and refined from electron diffraction tomography data [R1 = 18.8% for F > 4σ(F)] and further confirmed by synchrotron X-ray diffraction and density functional theory (DFT) calculations. The mineral is orthorhombic, space group Pnma and unit-cell parameters (synchrotron X-ray diffraction) are a = 7.2558(3), b = 27.992(1), c = 6.5243 (3) Å, V = 1325.10(8) Å3, Z = 4. The crystal structure of karibibbite consists of bands of Fe3+O6 octahedra running along a framed by two chains of AsO3 trigonal pyramids at each side, and along c by As2O5 dimers above and below. Each band is composed of ribbons of three edge-sharing Fe3+O6 octahedra, apex-connected with other ribbons in order to form a kinked band running along a. The atoms As(2) and As(3), each showing trigonal pyramidal coordination by O, share the O(4) atom to form a dimer. In turn, dimers are connected by the O(3) atoms, defining a zig-zag chain of overall (As3+O2)n-n stoichiometry. Each ribbon of (Fe3+O6) octahedra is flanked on both edges by the (As3+O2)n-n chains. The simultaneous presence of arsenite chains and dimers is previously unknown in compounds with As3+. The lone-electron pairs (4s2) of the As(2) and As(3) atoms project into the interlayer located at y = 0 and y = ½, yielding probable weak interactions with the O atoms of the facing (AsO2) chain.The DFT calculations show that the Fe atoms have maximum spin polarization, consistent with the Fe3+ state. |
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