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GEOREF RECORD

Maruyamaite, K(MgAl (sub 2) )(Al (sub 5) Mg)Si (sub 6) O (sub 18) (BO (sub 3) ) (sub 3) (OH) (sub 3) O, a potassium-dominant tourmaline from the ultrahigh-pressure Kokchetav Massif, northern Kazakhstan; description and crystal structure

Aaron Lussier, Neil A. Ball, Frank C. Hawthorne, Darrell J. Henry, Rentaro Shimizu, Yoshihide Ogasawara and Tsutomu Ota
Maruyamaite, K(MgAl (sub 2) )(Al (sub 5) Mg)Si (sub 6) O (sub 18) (BO (sub 3) ) (sub 3) (OH) (sub 3) O, a potassium-dominant tourmaline from the ultrahigh-pressure Kokchetav Massif, northern Kazakhstan; description and crystal structure
American Mineralogist (February 2016) 101 (2): 355-361

Abstract

Maruyamaite, ideally K(MgAl (sub 2) )(Al (sub 5) Mg)Si (sub 6) O (sub 18) (BO (sub 3) ) (sub 3) (OH) (sub 3) O, was recently approved as the first K-dominant mineral-species of the tourmaline supergroup. It occurs in ultrahigh-pressure quartzofeldspathic gneisses of the KumdyKol area of the Kokchetav Massif, northern Kazakhstan. Maruyamaite contains inclusions of microdiamonds, and probably crystallized near the peak pressure conditions of UHP metamorphism in the stability field of diamond. Crystals occur as anhedral to euhedral grains up to 2 mm across, embedded in a matrix of anhedral quartz and K-feldspar. Maruyamaite is pale brown to brown with a white to very pale-brown streak and has a vitreous luster. It is brittle and has a Mohs hardness of approximately 7; it is non-fluorescent, has no observable cleavage or parting, and has a calculated density of 3.081 g/cm (super 3) . In plane-polarized transmitted light, it is pleochroic, O=darkish brown, E=pale brown. Maruyamaite is uniaxial negative, omega =1.634, epsilon =1.652, both + or -0.002. It is rhombohedral, space group R3m, a=15.955(1), c=7.227(1) Aa, V=1593(3) Aa (super 3) , Z=3. The strongest 10 X-ray diffraction lines in the powder pattern are [d in Aa(I)(hkl)]: 2.581(100)(051), 2.974(85)(132), 3.995 (69)(240), 4.237 (59)(231), 2.046 (54)(162), 3.498 (42)(012), 1.923 (36)(372), 6.415 (23)(111), 1.595 (22)(5.10.0), 5.002 (21)(021), and 4.610(20)(030). The crystal structure of maruyamaite was refined to an R (sub 1) index of 1.58% using 1149 unique reflections measured with MoKalpha X-radiation. Analysis by a combination of electron microprobe and crystal-structure refinement gave SiO (sub 2) 36.37, Al (sub 2) O (sub 3) 31.50, TiO (sub 2) 1.09, Cr (sub 2) O (sub 3) 0.04, Fe (sub 2) O (sub 3) 0.33, FeO 4.01, MgO 9.00, CaO 1.47, Na (sub 2) O 0.60, K (sub 2) O 2.54, F 0.30, B (sub 2) O (sub 3) (calc) 10.58, H (sub 2) O(calc) 2.96, sum 100.67 wt%. The formula unit, calculated on the basis of 31 anions pfu with B=3, OH=3.24 apfu (derived from the crystal structure) and the site populations assigned to reflect the mean interatomic distances, is (K (sub 0.53) Na (sub 0.19) Ca (sub 0.26) [] (sub 0.02) ) (sub Sigma X=1.00) (Mg (sub 1.19) Fe (super 2+) (sub 0.55) Fe (super 3+) (sub 0.05) Ti (sub 0.14) Al (sub 1.07) ) (sub Sigma Y=3.00) (Al (sub 5.00) Mg (sub 1.00) )(Si (sub 5.97) Al (sub 0.03) O (sub 18) )( BO (sub 3) ) (sub 3) (OH) (sub 3) (O (super 2-) (sub 0.60) F (sub 0.16) OH (sub 0.24) ). Maruyamaite, ideally K(MgAl (sub 2) )(Al (sub 5) Mg)(BO (sub 3) ) (sub 3) (Si (sub 6) O (sub 18) )(OH) (sub 3) O, is related to oxy-dravite: ideally Na(MgAl (sub 2) )(Al (sub 5) Mg)(BO (sub 3) ) (sub 3) (Si (sub 6) O (sub 18) )(OH) (sub 3) O, by the substitution (super X) K--> (super X) Na.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 101
Serial Issue: 2
Title: Maruyamaite, K(MgAl (sub 2) )(Al (sub 5) Mg)Si (sub 6) O (sub 18) (BO (sub 3) ) (sub 3) (OH) (sub 3) O, a potassium-dominant tourmaline from the ultrahigh-pressure Kokchetav Massif, northern Kazakhstan; description and crystal structure
Affiliation: University of Manitoba, Department of Geological Sciences, Winnipeg, MB, Canada
Pages: 355-361
Published: 201602
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 67
Accession Number: 2016-025595
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 7 tables
N52°45'00" - N53°15'00", E68°30'00" - E70°19'60"
Secondary Affiliation: Louisiana State University, USA, United StatesWaseda University, JPN, JapanOkayama University, JPN, Japan
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: 201613
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