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

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, Larv...

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Bibliographic Details
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
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Summary: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.

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