Titre du document / Document title

New mineral bario-olgite, Ba(Na, Sr, REE)²Na[PO⁴]² and its crystal structure

Auteur(s) / Author(s)

PEKOV I. V. ; CHUKANOV N. V. ; KULIKOVA I. M. ; ZUBKOVA N. V. ; KROTOVA O. D. ; SOROKINA N. I. ; PUSHCRAROVSKY D. Yu. ;

Résumé / Abstract

New mineral bario-olgite, Ba-dominant analogue of olgite, was found in hyperagpaitic pegmatite «Palitra» at Mt. Kedykverpakhk, Lovozero alkaline massif, Kola Peninsula, Russia. It is associated with manaksite, natrosilite, villiaumite, aegirine, ussingite, sodalite, serandite, chkalovite, vuonnemite, etc. It occurs as grains up to 1.5 × 1 cm, rarely pyramidal-prismatic crystals (class 3) formed by faces: {100}, {-100{. {101}, {-101}, {10-1} and {-10-1}. Transparent, light green, streak white, lustre vitreous. Brittle, cleavage not observed. Mohs'hardness 4-4.5. Measured density 4.00, calculated 3.986 g/cm₃. Optically uniaxial, negative, oo 1.628, ε 1.623. Chemical composition (electron probe, wt%) is: Na²O 14.78, K²O 0.87, CaO 0.32, SrO 16.57, BaO 31.17, MnO 0.39, La²O³ 2.41, Ce²O³ 1.90, Pr²O³ 0.10, Nd²O³ 0.16, SiO² 0.08, P²O⁵ 31.77, total 100.52. The empirical formula calculated on O⁸ is: (Na^2.14K^0.08Ca^0.03Mn^0.02Sr^0.72Ba^0.91La^0.07Ce^0.05)^24.02P^2.01O⁸. The simlified formula (Z = 1): Ba(Na, Sr, REE)²Na[PO⁴]². Trigonal, P3. Unit cell dimensions: a = 5.549(1), c = 7.032(2) Å, V = 187.5(1) Å₃. The strongest reflexes of X-ray powder pattern (d, Å-I[hkl]) are: 7.044-22[001], 3.964-60[101, 011], 2.839-100[012], 2.774-100[110], 1.984-40[202], 1.611-26[21-2, 122]. IR spectrum is given. The crystal structure was refined on single crystal, R = 0.038. Isostructural with olgite but different cation distribution has been found. Isomorphism 2Sr₂₊ ↔ Na₊ + REE₃₊ allows to suppose an existence of the compound NaBa(Na^1.5REE^0.5)[PO⁴]² as Sr-free end-member of the olgite - banjo-olgite series. Type specimen is deposited in Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow.

Revue / Journal Title

Zapiski Vserossijskogo mineralogičeskogo obŝestva   ISSN 0869-6055 

Source / Source

2004, vol. 133, n^o1, pp. 41-49 [9 page(s) (article)]

Langue / Language

Russe

Editeur / Publisher

Nauka, Sankt-Peterburg, RUSSIE, FEDERATION DE  (1992) (Revue)

Localisation / Location

INIST-CNRS, Cote INIST : 4673, 35400011431856.0040