Remondite-(La), Na_3(La, Ce, Ca)_3(CO_3)_5—A new mineral of the burbankite family from khibiny massif, kola peninsula

摘要

Remondite--(La), Na_3(La, Ce, Ca)_3(CO_3)_5—A new mineral of the burbankite family has been found in aegirinecore of small hyperagpaitic pegmatite at Koashva Mt., Khibinyalkaline massif, Kola Peninsula. It associates with cancrisilite,microcline, sodalite, villiaumite, natrolite, natrolite, pectolite,lomonosovite, Ba-lamprophyllite, catapleiite, natron,thermonatrite, sazykinaite-(Y), Nb-rinkite, vitusite-(Ce),fluorcaphite. Rough-prismatic segregations (up to 2x0.8x0.5mm)of remondite-(La) consist of microporous chaotic aggregate oftiny (up to 5#mu#m) irregular grains. Translucent, colour is brightorange-yellow, streak white, lustre vitreous. Brittle, cleavage isabsent, fracture conchoidal, Mohs' hardness ~3. D_meas =3.5(1) ,D_calc =3.57g/cm~3. Optically biaxial, negative, 2V=_meas=80(10)deg, 2V_calc =85(5)deg; colourless, nonpleochroic.Refractive indexes: #alpha#=1.615(2), #beta# =1.619(3),#gamma# =1.622(3). Average chemical composition (electronprobe, CO_2 content is calculated by stoichiometry), wt%: Na_2O15.48, K_2O 0.58, CaO5.13, SrO2.93, BaO 0.18, Y_2O_3 16.67,Pr_2O_3 0.99, Nd_2O_3 2.27, Sm_2O_3 0.37, ThO_2 1.34,CO_2 (32.97); total 98.66. empirical formula:Na_2.87(La_0.805Ce_0.68Na_0.46Sr_0.18Nd_0.09K_0.08Pr_0.04Th_0.03Sm_0.01Ba_0.01)_?3.00(CO_3)_5. Monoclinic,P2_1(?). unit cell parameters: a =10.49(1), b =63417(4), c=10.50(1) A, #beta# =119.8 (1), V =613(1)A~3, Z =2. Thestrongest reflexes of x-ray powder diagram(d, A—I—hkl);3.70—7—012; 3.036—9—112, 211,311; 2.623—10—204, 022,402,220; 2.143—8—014,410; 2.041—6—222; 1.939—6—032,230. IR spectrum is geven. Type specimen is deposited inFersman Mineralogical Museum of Russian Academy of Sciences, Moscow.