• journal_title：American Mineralogist
• Contributor：Victor N. Yakovenchuk ; Gregory Yu. Ivanyuk ; Sergey V. Krivovichev ; Yakov A. Pakhomovsky ; Ekaterina A. Selivanova ; Julia A. Korchak ; Yuri P. Men’shikov ; Svetlana V. Drogobuzhskaya ; Oleg A. Zalkind
• Publisher：Mineralogical Society of America
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2011.3726
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：96
• issue：10
• firstpage：1624
• section：Articles

Eliseevite, Na_1.5Li[Ti₂Si₄O_12.5(OH)_1.5]·2H₂O, is a new microporous titanosilicate of the lintisite-kukisvumite family [monoclinic, C2/c, a = 27.48(1), b = 8.669(4), c = 5.246(2) Å, β = 90.782(8)°, V = 1249.7(9) ų, Z = 4]. The mineral is found in two different peralkaline veins in an ijolite–foyaite–malignite differentiated complex of the Lovozero alkaline massif, Kola Peninsula, Russia. At Mt. Alluaiv, eliseevite occurs in an aegirine-eudialyte-sodalite-microcline vein as long-prismatic to fibrous crystals (up to 2 mm long) growing in voids of natrolitized sodalite in close association with albite, analcime, catapleiite, chabazite-Ca, gmelinite-K, manganoneptunite, microcline, murmanite, and an ussingite. At Mt. Punkaruaiv, it is found within a ussingite-aegirine-microcline vein as long-prismatic crystals (up to 0.8 mm long) in close association with chabazite-Ca, chkalovite, eudialyte, manganoneptunite, punkaruaivite, rhabdophane-(Ce), sodalite, sphalerite, and steenstrupine-(Ce). It is a late-stage, hydrothermal mineral formed as a result of alteration of murmanite. The mineral is transparent, pale creamy to colorless, with a vitreous luster and a white streak. Cleavage is perfect along {100}, fracture is splintery. Mohs hardness is about 5. In transmitted light, the mineral is colorless, biaxial (−): α = 1.665(2), β = 1.712(2), γ = 1.762(5) (for λ = 589 nm); Y = b, Z^a = 8–12°. Dispersion is medium, r < v. D_calc = 2.706 g/cm³, D_meas = 2.68(4) g/cm³. The mean chemical composition (n = 7) determined by the Penfield method (water), ICP-MS (Li), and electron microprobe (other elements) is (wt%): H₂O 10.50, Li₂O 2.85, Na₂O 9.15, K₂O 0.08, CaO 0.05, Fe₂O₃ 0.21, Al₂O₃ 0.08, SiO₂ 46.87, TiO₂ 29.40, Nb₂O₅ 0.72, total 99.91. The empirical formula calculated on the basis of Si = 4 apfu is: (Na_1.51K_0.01Ca_0.01)_∑1.53Li_0.98[(Ti_1.89Nb_0.03Fe³⁺_0.01Al_0.01)_∑1.94Si₄O_12.26(OH)_1.74]·2.12H₂O. The simplified formula taking into account the results of a single-crystal study is Na_1.5Li{Ti₂O₂[Si₄O_10.5(OH)_1.5]}·2H₂O. The six strongest reflections in the X-ray powder-diffraction pattern [d in Å, (I), (hkl)] are: 13.76(100)(200), 6.296(60)(310), 3.577(80)(710), 3.005(70)(421), 2.881(70)(910), 2.710(50)(621̅). The mineral is named in honor of Nikolai Aleksandrovich Eliseev (1897–1966), a remarkable Russian geologist and petrologist, Professor at Leningrad State University, for his contributions to the geology and petrology of metamorphic and alkaline complexes.