• journal_title：The Canadian Mineralogist
• Contributor：Andrew M. McDonald ; George Y. Chao ; Joel D. Grice
• Publisher：Mineralogical Association of Canada
• Date：1994-
• Format：text/html
• Language：en
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：32
• issue：4
• firstpage：843
• section：Articles

Abenakiite-(Ce) is a new mineral species discovered at the Poudrette Quarry, Mont Saint-Hilaire, Quebec. It occurs as a single 2X1 mm pale brown ellipsoidal grain in association with aegirine, eudialyte, mangan-neptunite, polylithionite, serandite, and steenstrupine-(Ce). The streak is white, and the luster, vitreous. The mineral is brittle, with a conchoidal fracture and a poor {0001} cleavage. It displays no discernible fluorescence under long- or short-wave ultraviolet radiation, has a Mohs hardness greater than 4, and exhibits a very weak effervescence in 1:1 HCl. D(meas.) is 3.21, D(calc.) 3.27 g/cm ³ for the empirical formula. Abenakiite-(Ce) is uniaxial negative, omega 1.589(1) and epsilon 1.586(1). The average of four electron-microprobe analyses is Na ₂ O 25.32, Ce ₂ O ₃ 15.31, La ₂ O ₃ 5.94, Nd ₂ O ₃ 7.78, Pr ₂ O ₃ 2.02, Sm ₂ O ₃ 0.74, ThO ₂ 1.42, SrO 0.12, SiO ₂ 13.30, P ₂ O ₅ 14.11, SO ₂ 2.28, CO ₂ 8.90 (calc.), total 97.24 wt. %, corresponding to Na (sub 24.23) (Ce (sub 2.77) Nd (sub 1.37) La (sub 1.08) Pr (sub 0.36) Th (sub 0.16) Sm (sub 0.13) Sr (sub 0.03) ) (sub Sigma 5.90) Si (sub 6.56) P (sub 5.90) C ₆ S (sub 1.06) O ₆₃ on the basis of O = 63 or, ideally, Na ₂₆ REE ₆ (SiO ₃ ) ₆ (PO ₄ ) ₆ (CO ₃ ) ₆ (S (super 4+) O ₂ )O with Z = 3. It is rhombohedral, R3, with a 16.018(2), c 19.761(4) Aa, V 4390.9(1) Aa ³ . The strongest eight reflections in the X-ray powder pattern [d in Aa(I)(hkl)] are 11.414(75)(101), 8.036(85)(012), 6.554(85)(021), 4.646(75)(104), 3.773(90)(131), 3.591(80)(312), 3.150(70)(125), 2.674(100)(036). The name honors the Abenaki Indian Tribe, which inhabited the area around Mont Saint-Hilaire. The crystal structure has been refined to R = 3.1%, wR = 3.0% for 2116 observed [F>6sigma (F)] reflections. The structure, when viewed along c, may be best described in terms of a {6 ³ } hexagonal net, with chains of NaO ₇ polyhedra joined to PO ₄ groups at the nodes of the net and columns of six-membered SiO ₄ , NaO ₇ , and NaO ₇ -REEO ₈ polyhedral rings in the center. Within the columns are NaO ₆ octahedra, CO ₃ groups, and disordered SO ₂ groups.