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Chromo-alumino-povondraite, NaCr (sub 3) (Al (sub 4) Mg (sub 2) )(Si (sub 6) O (sub 18) )(BO (sub 3) ) (sub 3) (OH) (sub 3) O, a new mineral species of the tourmaline supergroup

Leonid Reznitskii, Christine M. Clark, Frank C. Hawthorne, Joel D. Grice, Henrik Skogby, Ulf Halenius and Ferdinando Bosi
Chromo-alumino-povondraite, NaCr (sub 3) (Al (sub 4) Mg (sub 2) )(Si (sub 6) O (sub 18) )(BO (sub 3) ) (sub 3) (OH) (sub 3) O, a new mineral species of the tourmaline supergroup
American Mineralogist (August 2014) 99 (8-9): 1767-1773

Abstract

Chromo-alumino-povondraite, NaCr (sub 3) (Al (sub 4) Mg (sub 2) )(Si (sub 6) O (sub 18) )(BO (sub 3) ) (sub 3) (OH) (sub 3) O, is a new mineral of the tourmaline supergroup. It is found in metaquartzites of the Pereval marble quarry (Sludyanka, Lake Baikal, Russia) in association with dravite, oxy-chromium-dravite, oxy-dravite, quartz, calcite, chromphyllite, eskolaite, chromite, uvarovite, chromian phlogopite, and pyroxenes of the diopside-kosmochlor series, Cr-bearing tremolite, Cr-bearing titanite, Cr-bearing rutile, and pyrite. Crystals are green and transparent with a vitreous luster, and exhibit a pale-green streak and conchoidal fracture. Chromo-alumino-povondraite has a Mohs hardness of approximately 7 1/2, and a calculated density of 3.227 g/cm (super 3) . In plane-polarized light, chromo-alumino-povondraite is pleochroic (O=emerald green and E=pale yellowish green) and uniaxial negative: omega =1.745(5), epsilon =1.685(5). Chromo-alumino-povondraite is rhombohedral, space group R3m, with the unit-cell parameters a=16.0277(2), c=7.3085(1) Aa, V=1625.93(5) Aa (super 3) , Z=3. Crystal-chemical analysis resulted in the empirical structural formula: X(Na (sub 0.87) Ca (sub 0.07) [] (sub 0.04) K (sub 0.02) ) (sub Sigma 1.00) Y(Cr (super 3+) (sub 2.29) Mg (sub 0.71) ) (sub Sigma 3.00) Z (Al (sub 3.04) Mg (sub 1.54) Cr (super 3+) (sub 1.18) V (super 3+) (sub 0.22) Fe (super 3+) (sub 0.01) ) (sub Sigma 6.00) [T(Si (sub 5.96) Al (sub 0.04) )O (sub 18) ] ( (super B) BO (sub 3) ) (sub 3) (super V) (OH) (sub 3) (super W) [O (sub 0.73) F (sub 0.25) (OH) (sub 0.02) ] (sub Sigma 1.00) The crystal structure of chromo-alumino-povondraite was refined to an R1 index of 1.68% using 1803 unique reflections collected with MoKalpha X-radiation. Ideally, chromo-alumino-povondraite is related to oxy-dravite and oxy-chromium-dravite by the homovalent substitution Cr (super 3+) <-->Al (super 3+) . Tourmaline with chemical compositions classified as chromo-alumino-povondraite can be either Al-dominant or Cr-dominant as a result of the compositional boundaries along the solid solution between Al and Cr (super 3+) that are determined at (super Y+Z) (Cr (sub 1.5) Al (sub 5.5) ), corresponding to Na (super Y) (Cr (sub 1.5) Al (sub 1.5) ) (super Z) (Al (sub 4) Mg (sub 2) )Si (sub 6) O (sub 18) (BO (sub 3) ) (sub 3) (OH) (sub 3) O, and (super Y+Z) (Cr (sub 5) Al (sub 2) ), corresponding to Na (super Y) (Cr (sub 3) ) (super Z) (Cr (sub 2) Al (sub 2) Mg (sub 2) )Si (sub 6) O (sub 18) (BO (sub 3) ) (sub 3) (OH) (sub 3) O.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 99
Serial Issue: 8-9
Title: Chromo-alumino-povondraite, NaCr (sub 3) (Al (sub 4) Mg (sub 2) )(Si (sub 6) O (sub 18) )(BO (sub 3) ) (sub 3) (OH) (sub 3) O, a new mineral species of the tourmaline supergroup
Affiliation: Russian Academy of Science, Institute of the Earth's Crust, Irkutsk, Russian Federation
Pages: 1767-1773
Published: 201408
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 49
Accession Number: 2014-104721
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 9 tables
N51°40'00" - N51°40'00", E103°40'00" - E103°40'00"
Secondary Affiliation: University of Manitoba, USA, United StatesCanadian Museum of Nature, CAN, CanadaSwedish Museum of Natural History, SWE, Sweden
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201452
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