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High-temperature in situ structural investigation on lead feldspar

Piera Benna, Mario Tribaudino and Emiliano Bruno
High-temperature in situ structural investigation on lead feldspar
American Mineralogist (February 1999) 84 (1-2): 120-129


Single-crystal X-ray diffraction was performed in situ at T = 20, 230, 465, and 700 degrees C on a partially ordered lead feldspar (PbAl (sub 2) Si (sub 2) O (sub 8) , I2/c, a = 8.402, b = 13.043, c = 14.308 Aa, beta = 115.30 degrees , V = 1417.6 Aa (super 3) ; Q (sub od) = 0.71). The unit-cell expansion (1.26X10 (super -5) degrees (super 1) ) is close to that observed for other feldspars, sanidine in particular, and occurs predominantly along a (super *) . The electron-density at the Pb site evolves with temperature toward a bean-like configuration close to that observed in disordered lead feldspar. The average Pb position approaches the c-glide plane with increasing temperature. Consequently the intensity of the b-type reflections reduces dramatically without evidence of an increase of Al-Si disorder. The evolution of atomic displacement parameters of the Pb atom with temperature supports the view that at room temperature Pb shows considerable positional disorder. Dark-field in situ TEM observations show that b antiphase domains (APD) persist unchanged in shape and size up to T = 690 degrees C. No diffuse component appears in b-type reflections in SAD patterns up to 935 degrees C, showing that the above changes in the Pb configuration do not affect the APD. The results suggest that, at T>700 degrees C, Pb reaches the glide plane assuming a configuration that may favor the Al-Si disorder.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 84
Serial Issue: 1-2
Title: High-temperature in situ structural investigation on lead feldspar
Affiliation: Dipartimento di Scienze Mineralogiche e Petrologiche, Turin, Italy
Pages: 120-129
Published: 199902
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 25
Accession Number: 1999-022427
Categories: Geophysics of minerals and rocks
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 7 tables
Secondary Affiliation: CNR Centro di Studi sulla Geodinamica delle Catene Collisionali, ITA, Italy
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 199908
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