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Publication Type
Journal Article
UWI Author(s)
Author, Analytic
Hassan, Ishmael
Author Affiliation, Ana.
Department of Chemistry
Article Title
Transmission electron microscopy and differential thermal studies of lazurite polymorphs
Medium Designator
n/a
Connective Phrase
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Journal Title
American Mineralogist
Translated Title
n/a
Reprint Status
Refereed
Date of Publication
2000
Volume ID
85
Issue ID
n/a
Page(s)
1383-89
Language
n/a
Connective Phrase
n/a
Location/URL
n/a
ISSN
n/a
Notes
n/a
Abstract
Transmission electron microscopy (TEM) and thermal (DTA-TG) analyses of lazurite, (Na,Ca)8[A16Si6O24](SO4,S)2, indicate three forms: cubic, modulated, and orthorhombic. Cubic lazurite contains mainly [Na3Ca.SO4]3+ clusters that are disordered together with the O1 and O2 oxygen atoms, and no satellite reflections occur. In the modulated lazurite structure, [Na3Ca.SO4]3+ and [Na3Ca.S]3+ clusters are ordered and possibly cause ordering of the framework oxygen atoms on the O1 and O2 positions and produce satellite reflections. Different ordering of these clusters gives an orthorhombic supercell with parameters of 2d1106d0c with respect to the cubic subcell. The DTA-TG study indicates that the orthorhombic to the modulated phase transition occurs at a peak temperature of 489C. A single-crystal fragment of lazurite may contain all three phases, as was observed by TEM in this study. Such intergrowrths indicate a continuous framework with different regions of the crystal containing different ordering and chemistries. Two new lazurite superstructures were obseved with dimensions of 6d1103d001, and 3d1123d with respect to the cubic subcell.....
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