Crystal Structure of Ilyukhinite, a New Mineral of the Eudialyte Group

The crystal structure of ilyukhinite, a new mineral of the eudialyte group, is studied by X-ray diffraction. The mineral found in pegmatite bodies of the Kukisvumchorr Mountain (Khibiny alkaline complex) is characterized by low sodium content, high degree of hydration, and predominance of manganese over iron. The trigonal cell has the following parameters: a = 14.1695(6) and c = 31.026(1) angstrom; space group R3m. The structure is refined to final R = 0.046 in the anisotropic approximation of atomic displacements using 1527F > 3 sigma F. The idealized formula of ilyukhinite (Z = 3) is written as (H3O,Na)(14)Ca6Mn2Zr3Si26O72(OH)(2) center dot 3H(2)O. The new mineral differs from other representatives of the eudialyte group by the predominance of both oxonium in the N positions of extra-framework cations and manganese in the M2 position centering the tetragonal pyramid.