The Crystal Structure of Kapustinite Na_(5.5)Mn_(0.25)ZrSi_6O_(16)(OH)_2: A New Mineral of the Lovozerite Group

摘要

The Na,Zr-silicate (lovozerite) discovered in the Lovozero alkaline massif (Kola Peninsula) more than 60 years ago served as the parent mineral for a large group of structurally cognate minerals. At present, the crystal structures of more than 15 natural and synthetic lovozerite-type compounds have been studied. They have the general crystallochemical formula A_3B_3C_2MSi_6O_9O_(9-x)(OH)_x and the following species-forming components: M = Zr, Ti, Fe~(3+); C = Ca, Mn, □; A, B = Na, □; and 0 ≤ x ≤ 6 1-6. The lovozerite structure includes six-membered Si-O rings linked by isolated M- and C-octahedra into a framework with cavities that are mainly occupied by large Na cations and occasional H_2O molecules.