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Na biotite and intermediate Na-K biotite in schists from the Betic Cordilleras, Spain

Maria Dolores Ruiz Cruz
Na biotite and intermediate Na-K biotite in schists from the Betic Cordilleras, Spain
Clays and Clay Minerals (October 2004) 52 (5): 603-612


Submicroscopic intergrowths of K biotite, Na biotite and intermediate Na-K biotite from a schist near Malaga (Betic Cordilleras, Spain) were discovered using high-resolution transmission electron microscopy and analytical electron microscopy. The sample was also studied with X-ray diffraction, electron microprobe analysis, and scanning electron microscopy. Scanning electron microscopy revealed that the Na-enriched biotite is concentrated in albite-rich microdomains, albite being partially replaced by biotite. These images also revealed that both K and Na-K biotite grains appear locally retrograded to kaolinite. Transmission electron microscopic data indicated that K biotite, Na biotite and Na-K biotite form parallel or subparallel packets with interfaces parallel to the basal planes of biotite. Potassium biotite forms thick packets, chemically homogeneous, with a basal spacing of 10.1 A. Sodium biotite also occurs as chemically homogeneous stacks of layers with a 9.78 A periodicity. Sodium-K biotite shows, on the contrary, variable composition and basal spacings intermediate between K and Na biotites. Analytical electron microscopic data revealed important chemical differences between Na and K biotites, which affect both the tetrahedral and the octahedral sheets. Both electron microprobe analysis and analytical electron microscopy indicated that the trioctahedral micas show relatively low interlayer occupancy, suggesting the presence of H (sub 3) O (super +) replacing the interlayer cations. Partial hydration of biotite explains the presence of a weak 14 Aa reflection in the X-ray patterns. Both chemical and textural data suggested that these trioctahedral micas grew during a common prograde metamorphic episode, the phases with intermediate composition probably being metastable.

ISSN: 0009-8604
EISSN: 1552-8367
Serial Title: Clays and Clay Minerals
Serial Volume: 52
Serial Issue: 5
Title: Na biotite and intermediate Na-K biotite in schists from the Betic Cordilleras, Spain
Affiliation: Universidad de Malaga, Departamento de Quimica Inorganica, Cristalografia y Mineralogia, Malaga, Spain
Pages: 603-612
Published: 200410
Text Language: English
Publisher: Clay Minerals Society, Clarkson, NY, United States
References: 30
Accession Number: 2005-004563
Categories: Mineralogy of silicatesIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, sketch map
N36°00'00" - N38°45'00", W05°34'60" - E00°15'00"
N36°17'60" - N37°17'60", W05°30'00" - W03°45'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200502
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