Crystal Structure of Magnesioferrikatophorite

D. Yu. Pushcharovski*, Yu. S. Lebedeva*, I. V. Pekov*, G. Ferraris**,
A. A. Novakova*, and G. Ivaldi**

* Moscow State University,
Leninskie gory, Moscow, 119992 Russia

** Department of Mineralogy and Petrology, University of Turin,
Via Valperga Caluso 35, Turin, 10125 Italy

Received May 20, 2002

Abstract—The crystal structure of the Na,Ca-amphibole magnesioferrikatophorite found in carbonatites from
the Turiy Cape (Kola Peninsula) was refined (Siemens P4 diffractometer, MoK radiation, 1481 independent
reflections with F > 4(F), anisotropic refinement, R(F) = 0.039). The parameters of the monoclinic unit cell
are a = 9.875(5) Å, b = 18.010(8) Å, c = 5.309(3) Å, = 104.39(5), sp. gr. C2/m, Z = 2. The distribution of the
cations over the crystallographically nonequivalent M(1–4)-positions was revealed by Mössbauer spectroscopy
and X-ray diffraction analysis. The character of splitting of the A-position correlates with the characteristic fea-
tures of the magnesioferrikatophorite composition. The resulting structural formula (Na_0.87K_0.13)₌₁
(Na_1.18Ca_0.82)₌₂(Mg_1.41)₌₂ (Mg_0.69)₌₂ (Mg_0.60Mn_0.02)₌₁(Si_3.16Al_0.84)₌₄
Si₄O₂₂(O_1.05O_0.66F_0.29)₌₂ agrees well with the electron microprobe analysis data. Based on the zonal char-
acter of the crystal and high Fe³⁺ content, the conditions of crystallogenesis are defined as oxidative against the
background of a decrease in the Na potential in the course of the evolution of a mineral-forming system. © 2003
MAIK “Nauka/Interperiodica”.

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