Meieranite, Na2Sr3MgSi6O17, a new mineral from the Wessels mine, Kalahari manganese fields, South Africa

Hexiong Yang, G. U. Xiangping, Robert T. Downs, Stanley H. Evans, Jaco J. Van Nieuwenhuizen, Robert M. Lavinsky, Xiande Xie

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Abstract

A new mineral species, meieranite, ideally Na2Sr3MgSi6O17, 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 0.5 3 0.5 3 0.4 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/cm3, respectively. Optically, meieranite is biaxial (–), with a ¼ 1.610(1), b ¼ 1.623(1), c ¼ 1.630(1) (white light), 2V (meas.) ¼ 70(1)8, 2V (calc.) ¼ 728. 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 Na1.96(Sr2.91Ba0.03Ca0.03Pb0.02)R2.99(Mg0.62Mn0.28Co0.07Fe0.01)R0.98Si6.03O17, which can be simplified to Na2Sr3MgSi6O17. Meieranite is orthorhombic, with space group P21nb and unit-cell parameters a 7.9380(2), b 10.4923(3), c 18.2560(6) Å, and V 1520.50(8) Å3. Its crystal structure is characterized by two kinds of layers that alternate along [010]: layers of corner-sharing SiO4and MO4tetrahedra (M¼ Mg, Mn, Co, Fe) and layers of NaO6and SrO8polyhedra. The tetrahedral layers consist of eight-, five-, and four-membered rings and are composed of [Si6O17] ribbons (parallel to [101]) linked together by MO4tetrahedra. Most remarkably, the structure of meieranite is topologically identical to that of the nordite group of minerals, which has the general chemical formula Na3SrRMSi6O17, where R ¼ Ce and La and M ¼ Zn, Fe, and Mn. Accordingly, chemically, meieranite may be obtained through the coupled substitution of 2Srfor (Naþþ R) in nordite.

Original languageEnglish (US)
Pages (from-to)457-466
Number of pages10
JournalCanadian Mineralogist
Volume57
Issue number4
DOIs
StatePublished - Jan 1 2019
Externally publishedYes

Keywords

  • Crystal structure
  • Meieranite
  • Nordite
  • Raman spectra
  • X-ray diffraction

ASJC Scopus subject areas

  • Geochemistry and Petrology

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    Yang, H., Xiangping, G. U., Downs, R. T., Evans, S. H., Van Nieuwenhuizen, J. J., Lavinsky, R. M., & Xie, X. (2019). Meieranite, Na2Sr3MgSi6O17, a new mineral from the Wessels mine, Kalahari manganese fields, South Africa. Canadian Mineralogist, 57(4), 457-466. https://doi.org/10.3749/canmin.1800067