Allanite and Other REE-Rich Epidote-Group Minerals

摘要: Epidote-group minerals rich in rare earth elements (REE), particular allanite, are common accessory phases igneous, metamorphic, metasomatic, and sedimentary rocks. Small amounts of REE present most epidote-group minerals, but allanite—and the related dissakisite, ferriallanite, dollaseite, khristovite androsite—the essential structural constituents. An important characteristic REE-rich is that their octahedrally coordinated M sites contain major divalent cations. This paper summarizes literature data for these discusses chemistry, occurrence, phase relations, petrologic geologic significance. The chapter emphasizes because it best-studied minerals. Epidote-group isolated silicon tetrahedra corner-sharing groups two tetrahedra, thus assigned to disilicate or sorosilicate family (for a detailed description structure, see Franz Liebscher 2004). formula A2M3(SiO4)(Si2O7)(O,F)(OH), simplified form A2M3Si3O11(O,F)(OH), which A = Ca, Sr, Pb2+, Mn2+, Th, REE3+, U, Al, Fe3+, Fe2+, Mn3+, Mg, Cr3+, V3+ (Deer et al. 1986). There structurally different sites, A(1) A(2), with coordination numbers, there three M(1), M(2), M(3), all (Ueda 1955; Dollase 1971). In trivalent accommodated endmember epidote both Ca. incorporation REE3+ commonly charge balanced by cation (Fe2+, Mg) substituted one (Table 1 …