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Order-disorder process in the tetrahedral sites of albite

Elisabetta Meneghinello, Alberto Alberti and Giuseppe Cruciani
Order-disorder process in the tetrahedral sites of albite
American Mineralogist (August 1999) 84 (7-8): 1144-1151

Abstract

The crystal structure of albite from Stintino, Sardinia, Italy, was refined at different degrees of disorder to determine the (Si-Al) order-disorder process. Eight X-ray structure refinements were performed on single-crystal data collected at room temperature, after heating at 1050-1090 degrees C for 3 to 12 days. Average long-range order coefficients S between 0.93 and 0.24 were obtained for different samples. The results indicate that in the (Si-Al) disordering process Al enriches the Tlm site more than T2o and T2m sites. This trend continues until both Tlo and Tlm are occupied by 30% of Al, and T2o and T2m by 20% of Al. No evidence of complete disorder in T1 and T2 sites has been experimentally found to date. The (Si-Al) disordering process induces a clockwise rotation of the four-membered rings of tetrahedra parallel to the (100) plane. An inverse linear relationship between the isotropic equivalent displacement parameter of the Na atom, B (sub eq) (Na), and S is interpreted as positional disorder of Na. The variations in the Na-O bond lengths with increasing disorder are explained by the related variations in the bond strengths of tetrahedral cations.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 84
Serial Issue: 7-8
Title: Order-disorder process in the tetrahedral sites of albite
Affiliation: Universita di Ferrara, Istituto di Mineralogia, Ferrara, Italy
Pages: 1144-1151
Published: 199908
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 34
Accession Number: 1999-066021
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 8 tables
N38°49'60" - N41°30'00", E08°15'00" - E09°45'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 199922
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