KAPUSTINITE, Na_(5.5)Mn_(0.25)ZrSi_6O_(16)(OH)_2, A NEW MINERAL FROM LOVOZERO MASSIF (KOLA PENINSULA) AND NEW DATA ON THE GENETIC CRYSTALLOCHEMISTRY OF THE LOVOZERITE GROUP

摘要

Kapustinite, a new mineral of the lovozerite group, was found in hyperagpaitic pegmatite named the Palitra (Palette) at Kedykverpakhk Mt., Lovozero alkaline massif, Kola peninsula, Russia. It is associated with microcline, aegirine, ussingite, sodalite, analcime, natrosilite, villiaumite, serandite, lomonosovite, kazakovite, etc. Occurs as isometric grains up to 4 cm and clusters up to 8 cm. Transparent to translucent. Dark cherry-coloured. Streak pa-le-lilac. Lustre vitreous. Brittle, cleavage not observed, fracture conchoidal. Mohs' hardness 6. D (meas.) is 2.78, D (calc.) is 2.815 g/cm~3. Optically biaxial, sometimes uniaxial (-), alpha 1.585, beta approx= gamma 1.589, 2 V (meas) < 5 deg. Chemical composition (electron probe, H_2O by modified Penfield method), wt. percent: Na_2O 24.42, K_2O 0.02, MgO 0.02, CaO 0.18, MnO 2.36, ZnO 0.05, Fe_2O_3 0.36, Y_2O_3 0.17, Ce_2O_3 0.20, Nd_2O_3 0.24, SiO_2 52.82, TiO_2 0.54, ZrO_2 16.38, UO_2 0.28, H_2O 2.80, Total 100.84. The empirical formula calculate on Si_6 is: Na_(5.38) Y_(0.01)Ce_(0.01)Nd_(0.01)U_(0.01)Ca_(0.02)Mn_(0.23)Fe_(0.03)Ti_(0.05)Zr_(0.91)Si_6O_(15.91)(OH)_(2.12). Simplified formula is: Na_(5.5)Mn_(0.25)ZrSi_6O_(16)(OH)_2(Z = 2). Crystal Structure was studied, R = 0.075. Monoclinic, C 2/m. Unit cell dimensions: a = 10 693(4), b = 10.299(4), c = 7.373(4) A, beta= 91.91(5)deg, V = 812(1) A~3. The strongest lines of X-ray powder pattern (d, A-I[hkl]) are 7.40-36[110, 001]; 5.313-51[200, 11-1]; 3.690-43[220, 002]; 3.342-84[22-1, 11-2]; 3.270-92[221, 112, 130], 2.652-100[400, 22-2], 2.58-91[222, 040], 1.849-39[440]. The IR spectrum is given. Kapustinite is named in the memory of Yu. L. Kapustin (1933--2002), mineralogist and petrologist who made great contribution to the study of alkaline massifs. Type specimen is deposited in Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow. Cation and anion isomorphism, causes of unstability of structures, mechanisms of decationization and hydration and genetic problems for lovozerite group minerals arc discussed. It is shown that litvinskite is formed as a product of kapustinite hydrothermal alteration.