{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,7]],"date-time":"2025-10-07T14:25:06Z","timestamp":1759847106966},"reference-count":21,"publisher":"Mineralogical Society","issue":"6","license":[{"start":{"date-parts":[[2018,7,5]],"date-time":"2018-07-05T00:00:00Z","timestamp":1530748800000},"content-version":"unspecified","delay-in-days":2773,"URL":"https:\/\/www.cambridge.org\/core\/terms"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Mineral. mag."],"published-print":{"date-parts":[[2010,12]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>Fluoro-potassic-magnesio-arfvedsonite, ideally <jats:sup>A<\/jats:sup>K<jats:sup>B<\/jats:sup>Na<jats:sub>2<\/jats:sub><jats:sup>c<\/jats:sup>(Mg<jats:sub>4<\/jats:sub>Fe<jats:sup>3+<\/jats:sup>)<jats:sup>T<\/jats:sup>Si<jats:sub>8<\/jats:sub>O<jats:sub>22<\/jats:sub><jats:sup>w<\/jats:sup>F<jats:sub>2<\/jats:sub>, has been found in a dyke \u223c25 km southwest of Monte Metocha, Xixano region, northeastern Mozambique. Fluoro-potassic-magnesio-arfvedsonite and low sanidine form a fine-grained mafic, ultrapotassic, peralkaline igneous rock without visible phenocrysts. The amphibole is brittle, has a Mohs hardness of 6 and a splintery fracture; it is non-fluorescent with perfect {110} cleavage and no observable parting, and has a calculated density of 3.174 gcm<jats:sup>\u22123<\/jats:sup>. In plane-polarized light, it is pleochroic, <jats:italic>X<\/jats:italic>= pale grey-green, <jats:italic>Y<\/jats:italic> = blue-green, <jats:italic>Z<\/jats:italic> = pale grey; <jats:italic>X<\/jats:italic> ^ c = 23.6\u00b0 (in \u03b2 obtuse), <jats:italic>Y<\/jats:italic> \u2016 <jats:italic>b, Z<\/jats:italic> ^ c = 66.4\u00b0 (in \u03b2 acute). Fluoro-potassic-magnesio-arfvedsonite is biaxial negative, \u03b1 = 1.652(2), \u03b2 = 1.658(2), \u03b3 = 1.660(2); 2V<jats:sub>obs<\/jats:sub> = 22.5(7)\u00b0, 2V<jats:sub>calc<\/jats:sub> = 30.2\u00b0. The unit-cell dimensions are <jats:italic>a =<\/jats:italic> 9.9591(4), <jats:italic>b =<\/jats:italic> 17.9529(7), c = 5.2867(2) \u00c5, \u03b2 = 104.340(1)\u00b0, V = 919.73(10) \u00c5<jats:sup>3<\/jats:sup>, <jats:italic>Z<\/jats:italic> = 2. The nine strongest X-ray diffraction lines in the experimental powder pattern are: <jats:italic>[d<\/jats:italic> in \u00c5(<jats:italic>I<\/jats:italic>)(<jats:italic>hkl<\/jats:italic>)]: 2.716(100)(151), 3.410(70)(131), 8.475(50)(110), 3.178(50)(310), 3.309(30)(240), 2.762(20)(<jats:inline-graphic xmlns:xlink=\"http:\/\/www.w3.org\/1999\/xlink\" mime-subtype=\"png\" xlink:href=\"S0026461X00055468_inline01.png\"\/>31), 2.549(20)(260), 2.351(10)(<jats:inline-graphic xmlns:xlink=\"http:\/\/www.w3.org\/1999\/xlink\" mime-subtype=\"png\" xlink:href=\"S0026461X00055468_inline01.png\"\/>51), 2.269(10)(331). Electron microprobe analysis gave: SiO<jats:sub>2<\/jats:sub> 54.25, A1<jats:sub>2<\/jats:sub>O<jats:sub>3<\/jats:sub> 0.03, TiO<jats:sub>2<\/jats:sub> 1.08, FeO 6.69, Fe<jats:sub>2<\/jats:sub>O<jats:sub>3<\/jats:sub> 8.07, MgO 13.99, MnO 0.32, ZnO 0.05, CaO 1.16, Na<jats:sub>2<\/jats:sub>O 6.33, K<jats:sub>2<\/jats:sub>O 5.20, F 2.20, H<jats:sub>2<\/jats:sub>O<jats:sub>calc<\/jats:sub> 0.74, sum 99.18 wt.%. The formula unit, calculated on the basis of 24 (O,OH,F) with (OH+F) = 2\u2212(2 Ti), is <jats:sup>A<\/jats:sup>Ka<jats:sub>0.98<\/jats:sub><jats:sup>B<\/jats:sup>(Na<jats:sub>1.18<\/jats:sub>Ca<jats:sub>0.18<\/jats:sub>)<jats:sub>\u22111.99<\/jats:sub><jats:sup>C<\/jats:sup>(Mg<jats:sub>3.07<\/jats:sub>Fe<jats:sub>0.83<\/jats:sub><jats:sup>2+<\/jats:sup>Mn<jats:sub>0.04<\/jats:sub>Al<jats:sub>0.01<\/jats:sub>Fe<jats:sub>0.90<\/jats:sub><jats:sup>3+<\/jats:sup>Ti<jats:sub>0.12<\/jats:sub>Zn<jats:sub>0.01<\/jats:sub>)<jats:sub>\u2211=4.98<\/jats:sub><jats:sup>T<\/jats:sup>Si<jats:sub>8<\/jats:sub>O<jats:sub>22<\/jats:sub><jats:sup>W<\/jats:sup>[Fi.o<jats:sub>3<\/jats:sub>(OH)<jats:sub>0.73<\/jats:sub>O<jats:sub>0.24<\/jats:sub>]<jats:sub>\u22112.00<\/jats:sub> and confirms the usual pattern of cation order in the amphibole structure. The presence of a significant oxo component (locally balanced by Ti at the M(1) site) is related to the crystallization conditions. The presence of Fe<jats:sup>3+<\/jats:sup> at the <jats:italic>T<\/jats:italic> sites, originally suggested for the holotype specimen, is discounted for this amphibole composition.<\/jats:p>","DOI":"10.1180\/minmag.2010.074.6.951","type":"journal-article","created":{"date-parts":[[2011,1,31]],"date-time":"2011-01-31T05:29:32Z","timestamp":1296451772000},"page":"951-960","source":"Crossref","is-referenced-by-count":7,"title":["Crystal structure and crystal chemistry of fluoro-potassic-magnesio-arfvedsonite from Monte Metocha, Xixano region, Mozambique, and discussion of the holotype from Quebec, Canada"],"prefix":"10.1180","volume":"74","author":[{"given":"R.","family":"Oberti","sequence":"first","affiliation":[]},{"given":"M.","family":"Boiocchi","sequence":"additional","affiliation":[]},{"given":"F. 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