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Shirokshinite K(NaMg (sub 2) )Si (sub 4) O (sub 10) F (sub 2) , a new mica with octahedral Na from Khibiny Massif, Kola Peninsula; descriptive data and structural disorder

Igor V. Pekov, Nikita V. Chukanov, Giovanni Ferraris, Gabriella Ivaldi, Dmitriy Yu. Pushcharovsky and Alexander E. Zadov
Shirokshinite K(NaMg (sub 2) )Si (sub 4) O (sub 10) F (sub 2) , a new mica with octahedral Na from Khibiny Massif, Kola Peninsula; descriptive data and structural disorder
European Journal of Mineralogy (June 2003) 15 (3): 447-454

Abstract

Shirokshinite, K(NaMg (sub 2) )Si (sub 4) O (sub 10) F (sub 2) , is the analogue of tainiolite, K(LiMg (sub 2) )Si (sub 4) O (sub 10) F (sub 2) , with the M1 octahedron fully occupied by Na instead of Li. It was found in the Kirovskii underground apatite mine (Kukisvumchorr Mountain, Khibiny massif, Kola Peninsula, Russia) as a late hydrothermal mineral in a small hyperalkaline pegmatite embedded in ristschorrite. Shirokshinite is associated with microcline, kupletskite, aegirine, natrolite, lorenzenite, calcite, remondite-(Ce), donnayite-(Y), mckelveyite-(Y) and galena. Crystals are usually skeletal and coarse hexagonal [001] prismatic. Shirokshinite is transparent to translucent, colourless to pale greyish, hardness Mohs' approximately 2.5; D(calc) = 2.922 g/cm (super 3) . Optically biaxial (-), alpha = 1.526(1), beta = 1.553(2); gamma = 1.553(2); 2V (sub meas) = -5(5) degrees , V (sub calc) = -0 degrees ; Y = b, Z approximately a, X c = 3(2) degrees . The IR spectrum of shirokshinite is unique even if close to that of tainiolite: in particular, the presence of Na (super +) instead of Li (super +) shifts some bands towards low-frequencies. Single-crystal diffraction data (MoKalpha -radiation) gave a = 5.269(2), b = 9.092(9), c = 10.198(3) Aa, beta = 100.12(7) degrees , Z = 2, 1M-polytype, space group C2/m. Structure anisotropic refinement converged R = 0.13 for 715 observed reflections. Evidence of stacking faults in the structure is discussed and compared with the so called Durovic effect. The very little ditrigonal distortion in spite of the large dimension of the Na octahedron is discussed in comparison with tainiolite. A critical revision of old published data indicating octahedral Na in micas shows that this hypothesis was biased by the low quality of the chemical analyses.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 15
Serial Issue: 3
Title: Shirokshinite K(NaMg (sub 2) )Si (sub 4) O (sub 10) F (sub 2) , a new mica with octahedral Na from Khibiny Massif, Kola Peninsula; descriptive data and structural disorder
Affiliation: Moscow State University, Faculty of Geology, Moscow, Russian Federation
Pages: 447-454
Published: 200306
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 28
Accession Number: 2003-055028
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 8 tables
N35°00'00" - N71°00'00", W25°00'00" - E75°00'00"
N67°00'00" - N68°00'00", E33°00'00" - E34°00'00"
N66°00'00" - N70°00'00", E32°00'00" - E42°00'00"
N37°00'00" - N83°00'00", W170°00'00" - E28°00'00"
Secondary Affiliation: Institute of Chemical Physics Problems, RUS, Russian FederationUniversita di Torino, ITA, ItalyNPO Regenerator, RUS, Russian Federation
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200318
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