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Meieranite, Na (sub 2) Sr (sub 3) MgSi (sub 6) O (sub 17) , a new mineral from the Wessels Mine, Kalahari manganese fields, South Africa

Hexiong Yang, Gu Xiangping, Robert T. Downs, Stanley H. Evans, Jaco J. Van Nieuwenhuizen, Robert M. Lavinsky and Xie Xiande
Meieranite, Na (sub 2) Sr (sub 3) MgSi (sub 6) O (sub 17) , a new mineral from the Wessels Mine, Kalahari manganese fields, South Africa
The Canadian Mineralogist (July 2019) 57 (4): 457-466

Abstract

A new mineral species, meieranite, ideally Na (sub 2) Sr (sub 3) MgSi (sub 6) O (sub 17) , has been found in the Wessels mine, Kalahari Manganese Fields, Northern Cape Province, South Africa. It occurs in isolated aggregates embedded in a matrix mainly of sugilite, along with minor aegirine and pectolite. Crystals of meieranite are up to 0.5X0.5X0.4 mm in size. No twinning is observed. The mineral is light blue to blue in transmitted and under incident lights, transparent with white streak, and has vitreous luster. It is brittle and has a Mohs hardness of 5.5; cleavage is good on {010} and no parting was observed. The measured and calculated densities are 3.41(3) and 3.410 g/cm (super 3) , respectively. Optically, meieranite is biaxial (-), with alpha =1.610(1), beta =1.623(1), gamma =1.630(1) (white light), 2V(meas.)=70(1) degrees , 2V(calc.)=72 degrees . The calculated compatibility index based on the empirical formula is -0.007 (superior). An electron microprobe analysis yields an empirical formula (based on 17 O apfu) of Na (sub 1.96) (Sr (sub 2.91) Ba (sub 0.03) Ca (sub 0.03) Pb (sub 0.02) ) (sub Sigma 2.99) (Mg (sub 0.62) Mn (sub 0.28) Co (sub 0.07) Fe (sub 0.01) ) (sub Sigma 0.98) Si (sub 6.03) O (sub 17) , which can be simplified to Na (sub 2) Sr (sub 3) MgSi (sub 6) O (sub 17) . Meieranite is orthorhombic, with space group P2 (sub 1) nb and unit-cell parameters a 7.9380(2), b 10.4923(3), c 18.2560(6) Aa, and V 1520.50(8) Aa (super 3) . Its crystal structure is characterized by two kinds of layers that alternate along [010]: layers of corner-sharing SiO (sub 4) and M (super 2+) O (sub 4) tetrahedra (M (super 2+) =Mg, Mn, Co, Fe) and layers of NaO (sub 6) and SrO (sub 8) polyhedra. The tetrahedral layers consist of eight-, five-, and four-membered rings and are composed of [Si (sub 6) O (sub 17) ] ribbons (parallel to [101]) linked together by MO (sub 4) tetrahedra. Most remarkably, the structure of meieranite is topologically identical to that of the nordite group of minerals, which has the general chemical formula Na (sub 3) SrR (super 3+) M (super 2+) Si (sub 6) O (sub 17) , where R=Ce and La and M=Zn, Fe, and Mn. Accordingly, chemically, meieranite may be obtained through the coupled substitution of 2Sr (super 2+) for (Na (super +) +R (super 3+) ) in nordite.


ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 57
Serial Issue: 4
Title: Meieranite, Na (sub 2) Sr (sub 3) MgSi (sub 6) O (sub 17) , a new mineral from the Wessels Mine, Kalahari manganese fields, South Africa
Affiliation: University of Arizona, Department of Geosciences, Tucson, AZ, United States
Pages: 457-466
Published: 20190715
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
References: 14
Accession Number: 2020-006646
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables
S26°06'52" - S26°06'52", E22°51'18" - E22°51'18"
Secondary Affiliation: Central South University, CHN, ChinaChinese Academy of Sciences, Guangzhou Institute of Geochemistry, CHN, China
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, copyright, Mineralogical Association of Canada. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202006
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