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Loparite is a complex oxide of Na, REE, Ti and Nb from the perovskite mineral group. Its general formula can be written as (Na,REE,Ca,Sr,Th)1-x(Ti,Nb,Ta)O3, where x designates vacancies in the A (large-cation) site. The chemical composition of loparite can change dramaticaly across a single crystal (see below). Its crystal structure is so flexible that it can adjust to various cationic substitutions via slight changes in symmetry (see here for details). This mineral does not just have spectacular chemical and structural flexibility, but also shows fantastic crystal shapes and zoning patterns. Shown here are:
[Upper right] Loparite twin (opaque) in nepheline syenite from Mt. Selsurt, Lovozero (Kola, Russia) as seen under the optical microscope. The associated colorless minerals are microcline, nepheline and eudialyte;
[Middle] Scanning-electron-microscopy images of loparite "flying saucer" penetration twin on  and random intergrowth of two cubo-octahedral loparite crystals; both are from tawite ("sodalite xenolith") from Mont Saint-Hilaire (Québec, Canada);
[Lower right] Back-scattered-electron image of loparite penetration twin with juxtaposed sectorial and oscillatory zoning patterns; this crystal is from an aegirine-feldspar vein in nepheline syenites, Khibiny (Kola, Russia).