From structure topology to chemical composition. VIII. Titanium silicates: the crystal chemistry of mosandrite from type locality of Låven (Skådön), Langesundsfjorden, Larvik, Vestfold, Norway

• Published in: Mineralogical Magazine
• Main Authors: Sokolova E, CAMARA ARTIGAS, Fernando
• Other Authors: Cámara F
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2008
• Subjects: mosandrite; rinkite; crystal structure; EMP analysi; chemical formula; Ti disilicate mineral; Group I; type locality; Greenland
• Online Access: http://hdl.handle.net/2318/128793; https://doi.org/10.1180/minmag.2008.072.4.887; http://minmag.geoscienceworld.org/content/72/4/887.abstract

The crystal structure of mosandrite, ideally Na(2)Ca(4)REETi(Si(2)O(7))(2)OF(3), a = 7.4184(8), b = 5.6789(6), c 18.873(2) angstrom, B = 101.410(2)degrees, V = 779.35(5) angstrom(3), space group P2(1)/c, Z = 2, D(calc) = 3.363 g.cm(-3), from the type locality, Laven (Skadon), Langesundsfjorden, Larvik, Vestfold, Norway, has been refined to R(1) = 6.33% on the basis of 1113 unique reflections |F(o) >= 4 sigma F|. Electron microprobe analysis gave the empirical formula Na(1.99)(Ca(3.93)Sr(0.02))(Sigma 3.95)(Ce(0.41)La(0.16)Nd(0.13)Pr(0.04)Sm(0.02)Dy(0.01)Y(0.13))(Sigma 0.90) (Ti(0.86)(4+)Nb(0.08)Zr(0.05))(Sigma 0.99)(Si(2)O(7))(2)(F(1.20)O(0.80))(Sigma 2.00)F(2), Z = 2, calculated on the basis of 18 (O + F) a.p.f.u. The crystal structure of mosandrite is a framework of TS (titanium silicate) blocks. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral). The TS block in mosandrite exhibits linkage and stereochemistry typical for Group 1 (Ti = 1 a.p.f.u.) Ti-disilicate minerals: two H sheets connect to the O sheet such that two (Si(2)O(7)) groups link to the trans edges of a Na polyhedron of the O sheet. The O sheet cations give Na(NaCa)Ti (4 a.p.f.u.). The TS blocks link via common vertices of Si(2)O(7)) groups and common vertices and edges of Ca-dominant M(H) and A(P) polyhedra. Two adjacent TS blocks are related by the glide plane c(y). Composition and topology of the TS block in mosandrite and rinkite are identical. The crystal structure of mosandrite from the type locality is topologically and chemically identical to that of rinkite from the type locality of Kangerdluarssuk, Greenland.