Amableite-(Ce), Na<sub>15</sub>[(Ce<sub>1.5</sub>Na<sub>1.5</sub>)Mn<sub>3</sub>]Mn<sub>2</sub>Zr<sub>3</sub>□Si[Si<sub>24</sub>O<sub>69</sub>(OH)<sub>3</sub>](OH)<sub>2</sub>⋅H<sub>2</sub>O, a new eudialyte-group mineral from Saint-Amable Sill, Québec, Canada
Nikita V. Chukanov, Andrey A. Zolotarev, Christof Schäfer, Д. А. Варламов, Igor V. Pekov, М. Ф. Вигасина, Dmitry I. Belakovskiy, Sergey M. Aksenov, S. A. Vozchikova, Sergey N. Britvin
Abstract
Abstract The new eudialyte-group mineral amableite-(Ce), ideally Na 15 [(Ce 1.5 Na 1.5 )Mn 3 ]Mn 2 Zr 3 □Si[Si 24 O 69 (OH) 3 ](OH) 2 ⋅H 2 O, was discovered in a peralkaline pegmatite at Saint-Amable Sill, Montérégie, Québec, Canada. The associated minerals are albite, microcline, aegirine, serandite, natrolite, yofortierite, and an unidentified titanosilicate forming minute grains. Amableite-(Ce) occurs as yellow equant or thick tabular crystals up to 2 mm across. The observed crystal forms are {0001}; the subordinate forms are {11 $\bar{2}$ 0}, {10 $\bar{1}$ 1}, and {10 $\bar{1}$ 0}. Amableite-(Ce) is brittle, with a Mohs hardness of 5. D (meas) = 2.89(1), D (calc) = 2.899 g⋅cm –3 . Amableite-(Ce) is optically anomalously biaxial (+) with α ≈ β = 1.603(2) and γ = 1.608(2). The chemical composition is (wt.%, electron microprobe, H 2 O measured by means of a modified Penfield method): Na 2 O 14.20, K 2 O 0.41, CaO 1.89, MnO 8.25, Fe 2 O 3 2.40, La 2 O 3 3.10, Ce 2 O 3 4.19, Pr 2 O 3 0.16, Nd 2 O 3 0.59, SiO 2 49.41, ZrO 2 11.17, HfO 2 0.24, TiO 2 0.68, Nb 2 О 5 1.54, Cl 0.26, H 2 O 1.70, –O≡Cl –0.06, total 100.13. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R 1 = 0.0423. Amableite-(Ce) is trigonal, space group R 3, with a = 14.1340(3) Å, c = 30.3780(11) Å and V = 5255.6(3) Å 3 . The crystal-chemical formula is (Na 12.93 K 0.27 Ce 0.06 ) Σ13.26 [(Mn 2.49 Ce 0.30 Ca 0.21 ) Σ3.00 (Ce 1.14 Na 1.04 Ca 0.82 ) Σ3.00 ](Mn 1.05 Fe 0.90 □ 1.05 ) Σ3.00 (Zr 2.85 Ti 0.12 Hf 0.03 ) Σ3.00 (□ 0.40 Nb 0.36 Si 0.24 ) Σ1.00 (Si 0.88 □ 0.12 ) Σ1.00 [Si 24 (O 70.44 (OH) 1.56 ) Σ72.00 ][(OH) 2.20 (H 2 O) 1.27 ] Σ3.47 Cl 0.22 ( Z = 3). Infrared and Raman spectra are given. The strongest lines of the powder X-ray diffraction pattern [ d , Å ( I , %)( hkl )] are: 11.34 (51)(101), 7.06 (76)(110), 4.312 (63)(205), 3.783 (38)(033), 3.538 (43)(027, 220), 2.963 (84)( $\bar{3}$ 45), 2.837 (100)(404). The mineral is named after the discovery locality.