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From structure topology to chemical composition; IX, Titanium silicates; revision of the crystal chemistry of lomonosovite and murmanite, Group-IV minerals

F. Camara, E. Sokolova, F. C. Hawthorne and Y. Abdu
From structure topology to chemical composition; IX, Titanium silicates; revision of the crystal chemistry of lomonosovite and murmanite, Group-IV minerals
Mineralogical Magazine (December 2008) 72 (6): 1207-1228

Abstract

The crystal structures of lomonosovite, ideally Na (sub 10) Ti (sub 4) (Si (sub 2) O (sub 7) ) (sub 2) (PO (sub 4) ) (sub 2) O4, a = 5.4170(7) Aa, b = 7.1190(9) Aa, c = 14.487(2) Aa, alpha = 99.957(3) degrees , beta = 96.711(3) degrees , gamma = 90.360(3) degrees , V = 546.28(4) Aa (super 3) , D (sub calc.) = 3.175 g cm (super -3) , and murmanite, ideally Na (sub 4) Ti (sub 4) (Si (sub 2) O (sub 7) ) (sub 2) O (sub 4) (H (sub 2) O) (sub 4) , a = 5.3875(6) A b = 7.0579(7) Aa, c = 12.176(1) Aa, alpha = 93.511(2) degrees , beta = 107.943(4) degrees , gamma = 90.093(2) degrees , V = 439.55(2) Aa (super 3) , D (sub calc.) = 2.956 g.cm (super -3) , from the Lovozero alkaline massif, Kola Peninsula, Russia, have been refined in the space group P1 (Z = 1) to R values of 2.64 and 4.47%, respectively, using 4572 and 2222 observed F (sub o) > or = 4sigma F reflections collected with a single-crystal Bruker AXS SMART APEX diffractometer with a CCD detector and Mo-K{alpha} radiation. Electron microprobe analysis gave empirical formulae for lomonosovite calculated on the basis of 26(O+F) a.p.f.u., and murmanite Z = 1, calculated on the basis of 22(O+F) a.p.f.u., with H (sub 2) O determined from structure refinement and Fe (super 3+) /(Fe (super 2+) +Fe (super 3+) ) ratios obtained by Mossbauer spectroscopy. The crystal structures of lomonosovite and murmanite are a combination of a titanium silicate (TS) block and an intermediate (I) block. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral), and is characterized by a planar cell based on translation vectors, t (sub 1) and t (sub 2) , with t (sub 1) approximately 5.5 and t (sub 2) approximately 7 Aa and t (sub 1) t (sub 2) close to 90 degrees . The TS block exhibits linkage and stereochemistry typical for Group IV (Ti = 4 a.p.f.u.) of the Ti disilicate minerals: two H sheets connect to the O sheet such that two (Si (sub 2) O (sub 7) ) groups link to Ti polyhedra of the O sheet adjacent along t (sub 1) . In murmanite and lomonosovite, the invariant part of the TS block is of composition Na (sub 4) Ti (sub 4) (Si (sub 2) O (sub 7) ) (sub 2) O (sub 4) . There is no evidence of vacancy-dominant cation sites or (OH) groups in the O sheet of lomonosovite or murmanite. In lomonosovite, the I block is a framework of Na polyhedra and P tetrahedra which gives 2[Na (sub 3) (PO) (sub 4) ] p.f.u. In murmanite, there are four (H (sub 2) O) groups in the intermediate space between TS blocks. In lomonosovite, TS and I blocks alternate along c. In murmanite, TS blocks are connected via hydrogen bonding. The H atoms were located and details of the hydrogen bonding are discussed.


ISSN: 0026-461X
EISSN: 1471-8022
Coden: MNLMBB
Serial Title: Mineralogical Magazine
Serial Volume: 72
Serial Issue: 6
Title: From structure topology to chemical composition; IX, Titanium silicates; revision of the crystal chemistry of lomonosovite and murmanite, Group-IV minerals
Affiliation: University of Manitoba, Department of Geological Sciences, Winnipeg, MB, Canada
Pages: 1207-1228
Published: 200812
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 42
Accession Number: 2010-023225
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 12 tables
N66°00'00" - N70°00'00", E32°00'00" - E42°00'00"
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 201014
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