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Natural kalsilite, KAlSiO (sub 2) , and P31c symmetry; crystal structure and twinning

Daniela Cellai, Paola Bonazzi and Michael A. Carpenter
Natural kalsilite, KAlSiO (sub 2) , and P31c symmetry; crystal structure and twinning
American Mineralogist (April 1997) 82 (3-4): 276-279

Abstract

A new KAlSiO (sub 4) polymorph was found in a granulite facies gneiss from the Punalur district, southern India. The structure was solved and refined on a twinned crystal to an R index value of 1.98% for 265 independent reflections. Metamorphic kalsilite is trigonal, space group P31c with a = 5.157 (1) Aa, b = 8.706 (3) Aa, V = 200.52 (9) Aa (super 3) , Z = 2. The overall diffraction symmetry 6/mmm exhibited from all the crystals examined arises from a {0001} twinning, related to a mistake in the ordered Al-Si-Al-Si sequence along the c axis. The crystal structure is a stuffed derivate of tridymite, and is characterized by six-membered tetrahedral rings with ditrigonal shape. Individual layers of this structure are the same as those of P6 (sub 3) kalsilite, but are stacked along the c axis in an eclipsed manner rather than in the staggered manner of the P6 (sub 3) structure.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 82
Serial Issue: 3-4
Title: Natural kalsilite, KAlSiO (sub 2) , and P31c symmetry; crystal structure and twinning
Affiliation: Dipartimento di Scienze della Terra, Florence, Italy
Pages: 276-279
Published: 199704
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 23
Accession Number: 1997-042330
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: 4 tables
N07°00'00" - N37°00'00", E68°00'00" - E97°00'00"
Secondary Affiliation: University of Cambridge, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 199715
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