• journal_title：American Mineralogist
• Contributor：Sergey V. Krivovichev ; Yakov A. Pakhomovsky ; Gregory Yu. Ivanyuk ; Julia A. Mikhailova ; Yuri P. Men’shikov ; Thomas Armbruster ; Ekaterina A. Selivanova ; Nicolas Meisser
• Publisher：Mineralogical Society of America
• Date：2007-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2007.2488
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：92
• issue：8-9
• firstpage：1525
• section：Articles

Yakovenchukite-(Y), K₃NaCaY₂[Si₁₂O₃₀](H₂O)₄, is a new REE silicate found in a thin (3–4 cm) sodalite-aegirine-microcline veinlet cutting ijolite-urtite at Mt. Kukisvumchorr, Khibiny alkaline massif, Kola Peninsula, Russia. The mineral occurs as small prismatic crystals in intimate association with microcline, aegirine, calcite, catapleiite, donnayite-(Y), fl uorapophyllite, fluorite, galena, lead, litharge, molybdenite, natrolite–gonnardite, pyrochlore, rinkite, strontianite, and vuorijarvite-K. Yakovenchukite-(Y) is creamy to colorless, with vitreous luster. The streak is white. The mineral is transparent, non-fluorescent. The Mohs hardness is about 5. The mineral is brittle. Cleavage is perfect on {100}, distinct on {010}, fracture is stepped. Densities are 2.83 g/cm³ (measured by sink/fl oat in heavy liquids) and 2.72 g/cm³ (calculated). Yakovenchukite-(Y) is biaxial (+): n_α = 1.520(5), n_β = 1.525(5), n_γ = 1.538(5) (589 nm), 2V(meas.) = 60 ± 5°, 2V(calc.) = 61.86°. The optical orientation is Y = ng>cng>, X = ng>ang>, Z = ng>bng>, pleochroism is not observed. Chemical analysis by electron microprobe (wt%): Na₂O 4.32, K₂O 10.73, CaO 3.42, Y₂O₃ 15.49, Ce₂O₃ 0.10, Dy₂O₃ 0.68, Er₂O₃ 0.88, Tm₂O₃ 0.18, Yb₂O₃ 1.53, ThO₂ 0.62, SiO₂ 57.55, H₂O (by the Penfield method) 4.70, total 100.20. The empirical formula (based on Si = 12 apfu) is (K_2.85 Na_0.15)_Σ3.00 Na_1.00 (Ca_0.71 Na_0.60)_Σ1.31 (Y_1.72 Yb_0.10 Er_0.06 Dy_0.05 Th_0.03 Ce_0.01 Tm_0.01 Ca_0.05)_Σ2.03 [Si₁₂ O_30.02]·3.27H₂O. According to single-crystal X-ray study yakovenchukite-(Y) is orthorhombic, Pcca, a = 14.972(8), b = 14.137(7), c = 14.594(8) Å, V = 3089(3) ų, Z = 4. The strongest lines of the X-ray powder diffraction pattern are [ d_bs(Å) (I_obs) (hkl)]: 7.00 (40) (020), 6.57 (60) (102), 4.20 (50) (222), 3.337 (100) (331), 3.248 (90) (024), 3.101 (40) (142), 3.014 (80) (422), 2.608 (40) (404). The crystal structure of yakovenchukite-(Y) belongs to a new structure type of minerals and inorganic compounds. It is based on microporous octahedral-tetrahedral framework of SiO₄-tetrahedra and YO₆-octahedra. Silicate tetrahedra share corners to form unprecedented [Si₁₂O₃₀] sheets consisting of 4-, 6-, and 14-membered rings. The sheets are parallel to (001) and are linked into 3D framework through YO₆ octahedra. Ca²⁺, K⁺, and Na⁺ cations are located within the framework cavities. The octahedral-tetrahedral framework possess channels extended along the ng>ang> axis. The channel dimensions are 4.9 × 6.2 Å, which means the free crystallographic diameter of 2.2 × 3.5 Å, that allows classifying yakovenchukite-(Y) as a microporous material. Yakovenchukite-(Y) is the latest low-temperature hydrothermal mineral, formed by alteration of earlier REE-rich minerals (pyrochlore, rinkite, etc.). The mineral is named in honor of Victor N. Yakovenchuk, a mineralogist at the Geological Institute of the Kola Science Centre of the Russian Academy of Sciences, for his outstanding contribution to the mineralogy of alkaline and alkaline-ultrabasic massifs.