• journal_title：European Journal of Mineralogy
• Contributor：Zhuming Yang ; Gerald Giester ; Kuishou Ding ; Ekkehart Tillmanns
• Publisher：E. Schweizerbart'sche Verlagsbuchhandlung Science Publishers
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.1127/0935-1221/2011/0023-2075
• journal_abbrev：Eur J Mineral
• issn：0935-1221
• volume：23
• issue：1
• firstpage：63
• section：Articles

Nanlingite was first described as a new mineral from a dolomitic limestone along a contact between greisenized granite and dolomitic limestone in the Nanling area, Hunan Province, China. The structure was solved and refined on single-crystal X-ray data in space group R 3̅m, with a = 10.2114(10), c = 25.689(3) Å, V = 2319.2(6) Å ³, to R1 = 0.021, wR2 = 0.049. The chemical formula of nanlingite is Na(Ca, Li, Na)₆(Mg, Fe)₁₂(AsO₃)₂[Fe(AsO₃)₆] F₁₄ with Z = 3 according to the crystal structure refinement.

The complex framework is formed by edge- and corner-sharing of distorted NaF₈ and CaF₄O₄ cubes, MgF₂O₄ octahedra, and AsO₃ trigonal pyramids. The lithium atom occupies (22 %) the split site at 0.58(2) Å from the main Ca site and exhibits a five-fold coordination with <Li–(O,F) > 2.21 Å. The iron atom (at 3b, site symmetry 3̅m) is surrounded by six As atoms of AsO₃ groups at a distance of 2.40 Å with the lone-pair electrons pointing towards the central atom. This [Fe(AsO₃)₆] cluster is a novel configuration in the crystal chemistry of minerals. According to Mössbauer spectra and electron energy-loss spectroscopy data the oxidation state of Fe in nanlingite is mainly Fe^II with a low-spin state. In the configuration of arsenite groups, the distance <As(2)–O>= 1.73 Å of the [Fe(AsO₃)₆] clusters is shorter than the normal range. The empirical crystal-chemical formula for nanlingite is (Na_0.90Li_0.10)∑_1.00(Ca_4.41 Li_1.06 Mg_0.17 Na_0.06 Mn_0.05 □_0.25)∑_6.00(Mg_11.38 Fe³⁺ _0.30Al_0.29Ti_0.03)∑_12.00 (AsO₃)₂ [Fe ^II (AsO₃)₆](F_13.77OH_0.16)∑_13.93.