• journal_title：The Canadian Mineralogist
• Contributor：Mark A. Cooper ; Yassir A. Abdu ; Neil A. Ball ; Petr Černý ; Frank C. Hawthorne ; Roy Kristiansen
• Publisher：Mineralogical Association of Canada
• Date：2012-08-01
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.50.4.793
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：50
• issue：4
• firstpage：793
• section：Mineralogy, Crystal Structure and Crystal Chemistry

d="p-1">Aspedamite, ideally □<sub>12sub>(Fe<sup>3+sup>,Fe<sup>2+sup>)<sub>3sub>Nb<sub>4sub>[Th(Nb,Fe<sup>3+sup>)<sub>12sub>O<sub>42sub>]{(H<sub>2sub>O),(OH)}<sub>12sub>, is a new heteropolyniobate mineral species from the Herrebøkasa quarry, Aspedammen, Østfold, southern Norway. It occurs as small euhedral crystals of dodecahedra and cubes to a maximum of 50 μm across, perched on a white mat of an Al–Nb–Fe–Ti–Ca–K-bearing silicate on a partly altered 12 × 12 × 6 mm crystal of monazite penetrated by plates of columbite-(Fe) and muscovite. Aspedamite is brownish orange with a very pale orange streak and an adamantine luster; it does not fluoresce under ultraviolet light. The Mohs hardness is 3–4, and it is brittle with a hackly fracture. The calculated density is 4.070 g/cm<sup>3sup>, and the calculated index of refraction is 2.084. Aspedamite is cubic, space group Im3̅, a 12.9078(6) Å, V 2150.6(3) Å<sup>3sup>, Z = 2. The strongest seven lines in the X-ray powder-diffraction pattern [d in Å(I)hkl] are: 9.107(100)011, 2.635(36)224, 2.889(33)024, 1.726(29)246, 3.233(28)004, 3.454(18)123, 4.567(15)022. A chemical analysis with an electron microprobe gave Nb<sub>2sub>O<sub>5sub> 65.64, Ta<sub>2sub>O<sub>5sub> 1.78, SiO<sub>2sub> 0.78, ThO<sub>2sub> 5.64, TiO<sub>2sub> 2.15, Fe<sub>2sub>O<sub>3sub> 10.56, FeO 2.73, MnO 0.82, CaO 0.28, K<sub>2sub>O 0.16, La<sub>2sub>O<sub>3sub> 0.52, Ce<sub>2sub>O<sub>3sub> 1.62, Nd<sub>2sub>O<sub>3sub> 0.44, H<sub>2sub>O (calc) 7.20, sum 100.32 wt.%; the H<sub>2sub>O content was determined by crystal-structure analysis. The empirical formula of aspedamite on the basis of 54 anions with Fe<sup>3+sup>/(Fe<sup>3+sup> + Fe<sup>2+sup>) = 0.67 (estimated from crystal-chemical arguments) and O(4) = (H<sub>2sub>O)<sub>9sub> + (OH)<sub>3sub> is K<sub>0.09sub> Ca<sub>0.13sub>Ce<sub>0.26sub>La<sub>0.08sub>Nd<sub>0.07sub>Fe<sup>2+sup><sub>1.00sub>Mn<sub>0.30sub>Fe<sup>3+sup><sub>3.48sub>Th<sub>0.56sub>Ti<sup>4+sup><sub>0.71sub>Si<sub>0.34sub>Nb<sub>12.98sub>Ta<sub>0.21sub>O<sub>42sub>(H<sub>2sub>O)<sub>9sub>(OH)<sub>3sub>. The crystal structure of aspedamite was solved by direct methods and refined to an R<sub>1sub> index of 1.6% based on 596 observed reflections collected on a three-circle rotating-anode (MoKα X-radiation) diffractometer equipped with multilayer optics and an APEX-II detector. The structure is based on the heteropolyanion [DA<sub>12sub>O<sub>42sub>] (D = Th, sum A = Nb<sub>9sub>Fe<sup>3+sup><sub>2sub>Ti), which consists of twelve face- and corner-sharing AO<sub>6sub> octahedra that surround the [12]-coordinated D cation. There are eight heteropolyanions at the corners of the unit cell, with an additional heteropolyanion at the center, forming an I-centered arrangement. Each heteropolyhedral cluster is decorated by eight B octahedra, each of which bridges two adjacent clusters along the body diagonals of the cell. Further intercluster linkage is provided by the C octahedra, which link pairs of adjacent clusters in the a direction. Aspedamite is isostructural with menezesite.