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MEIERANITE, Na2sr3mgsi6o17, a NEW MINERAL from the WESSELS MINE, KALAHARI MANGANESE FIELDS, SOUTH AFRICA

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MEIERANITE, Na2sr3mgsi6o17, a NEW MINERAL from the WESSELS MINE, KALAHARI MANGANESE FIELDS, SOUTH AFRICA 457 The Canadian Mineralogist Vol. 57, pp. 457-466 (2019) DOI: 10.3749/canmin.1800067 MEIERANITE, Na2Sr3MgSi6O17, A NEW MINERAL FROM THE WESSELS MINE, KALAHARI MANGANESE FIELDS, SOUTH AFRICA § HEXIONG YANG Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721-0077, USA XIANGPING GU School of Geosciences and Info-Physics, Central South University, Changsha, Hunan 410083, China ROBERT T. DOWNS AND STANLEY H. EVANS Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721-0077, USA JACO J. VAN NIEUWENHUIZEN Plot 968, Alheit, Kakamas 8870, Northern Cape, South Africa ROBERT M. LAVINSKY P.O. BOX 830460, Richardson, Texas 75083, USA XIANDE XIE Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, CAS, and Guangdong Key Laboratory of Mineral Physics and Materials, Guangzhou 510640, China 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)ofNa1.96(Sr2.91Ba0.03 Ca0.03Pb0.02)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) A, and V 1520.50(8) A˚ 3. Its crystal structure is characterized by two kinds of layers that alternate along [010]: layers of corner- 2þ 2þ sharing SiO4 and M O4 tetrahedra (M ¼ Mg, Mn, Co, Fe) and layers of NaO6 and SrO8 polyhedra. The tetrahedral layers consist of eight-, five-, and four-membered rings and are composed of [Si6O17] ribbons (parallel to [101]) linked together by MO4 tetrahedra. Most remarkably, the structure of meieranite is topologically identical to that of the nordite group of minerals, 3þ 2þ which has the general chemical formula Na3SrR M Si6O17, where R ¼ Ce and La and M ¼ Zn, Fe, and Mn. Accordingly, chemically, meieranite may be obtained through the coupled substitution of 2Sr2þ for (Naþ þ R3þ) in nordite. Keywords: meieranite, nordite, crystal structure, X-ray diffraction, Raman spectra. § Corresponding author e-mail address: [email protected] Downloaded from https://pubs.geoscienceworld.org/canmin/article-pdf/57/4/457/4800091/i1499-1276-57-4-457.pdf by University of Arizona user on 15 September 2019 458 THE CANADIAN MINERALOGIST INTRODUCTION nearly perfect semiconductor crystals. He is also an advocate of education and was responsible for the Intel A new mineral species, meieranite, ideally International Science and Engineering Fair (IISEF), Na2Sr3MgSi6O17, has been found in the Wessels mine, helping to expand and promote scientific literacy in Kalahari Manganese Fields, Northern Cape Province, youths. Gene started collecting minerals in 1949, with Republic of South Africa. It is named in honor of Dr. his present specialization in high-quality gem species Eugene Stuart Meieran, a member of the U.S. National and native silver. In addition to his time serving on Academy of Engineering. Gene received his M.S. and boards of several mineral museums, Gene has donated Sc.D. in Materials Science from the Massachusetts a number of important specimens to major museums, Institute of Technology in 1963. Since then, he has including Harvard, the Smithsonian, University of worked on many of the important problems that Arizona, Rice, and Yale. For his work in mineral impacted the emerging semiconductor industry, in- preservation and education, he was awarded the cluding purification, analyses, and quality control for prestigious Carnegie Medal in 2004 by The Carnegie the raw materials required for modern microchips. Museum. Gene is a co-founder of the science session Gene joined Intel Corp. in 1973 and was named Fellow at the Dallas Mineral Collectors Symposium. Recent- in 1984 and Senior Intel Fellow in 2003. He has ly, he helped found a new mineral museum in Los approximately 60 technical publications, of which 20 Angeles, California. The new mineral and its name are about X-ray topographic studies of defects in have been approved by the Commission on New TABLE 1. ELECTRON MICROPROBE ANALYSIS DATA FOR MEIERANITE Constituent wt.% Range Stand. Dev. Probe Standard SiO2 46.16 45.52–46.74 0.42 SiO2 CaO 0.21 0.18–0.25 0.03 CaMgSi2O6 MgO 3.21 2.74–4.29 0.53 MgO MnO 2.53 1.59–3.52 0.64 MnSiO3 FeO 0.10 0.00–0.26 0.08 Fe2SiO4 Na2O 7.75 7.52–8.11 0.17 NaAlSi3O8 SrO 38.39 38.07–38.97 0.26 SrSO4 BaO 0.52 0.25–0.90 0.23 BaSO4 CoO 0.69 0.41–0.81 0.13 CoO PbO 0.56 0.23–0.83 0.23 Pb5(VO4)3Cl Total 100.12 99.46–100.62 0.47 FIG. 1. Rock samples on which aggregates of granular blue meieranite crystals are found. Associated minerals are massive pale green sugilite, prismatic grey aegirine, and FIG. 2. A microscopic view of meieranite, associated with bladed white pectolite. pale green sugilite. Downloaded from https://pubs.geoscienceworld.org/canmin/article-pdf/57/4/457/4800091/i1499-1276-57-4-457.pdf by University of Arizona user on 15 September 2019 MEIERANITE, A NEW MINERAL FROM THE WESSELS MINE, SOUTH AFRICA 459 TABLE 2. POWDER X-RAY DIFFRACTION DATA FOR Minerals, Nomenclature and Classification (CNMNC) MEIERANITE of the International Mineralogical Association (IMA 2015-009). The cotype samples have been deposited at Imeas % Ical % dmeas dcalc hk lthe University of Arizona Mineral Museum (Catalogue 3.6 12.0 7.276 7.276 1 0 1 # 20011) and the RRUFF Project (deposition # 6.4 14.6 4.828 4.826 1 0 3 R140947). 3.4 2.2 4.547 4.541 0 2 2 This paper describes the physical and chemical 15.4 22.2 4.253 4.250 1 2 1 properties of meieranite and its crystal structure 5.1 3.8 3.962 3.967 2 0 0 determined from single-crystal X-ray diffraction data, 25.1 41.6 3.550 3.549 1 2 3 demonstrating that the structure of meieranite exhibits 11.3 16.7 3.436 3.439 0 2 4 all principal features of the nordite structural type. 42 33.3 3.166 3.162 2 2 0 100 100.0 2.990 2.988 2 2 2 SAMPLE DESCRIPTION AND EXPERIMENTAL METHODS 83.9 98.1 2.800 2.801 1 2 5 26.4 15.2 2.623 2.619 0 4 0 Occurrence, physical and chemical properties, and 9.9 16.2 2.474 2.475 1 0 7 Raman spectra 17.2 25.6 2.425 2.425 3 0 3 9.2 8.4 2.391 2.389 2 2 5 The type sample of meieranite was found on a 7 5.7 2.361 2.361 3 2 0 specimen collected from the Wessels mine, Kalahari 5.3 2.4 2.341 2.341 3 2 1 Manganese Fields, Northern Cape Province, Republic 4.5 3.5 2.306 2.302 1 4 3 of South Africa (2786051.8200 S, 22851018.3100 E). It 3.2 0.1 2.287 2.280 0 0 8 occurs in isolated aggregates embedded in a matrix 5.6 5.6 2.201 2.201 3 2 3 consisting of mainly pale-green sugilite, along with 21.2 15.4 2.126 2.125 2 4 2 minor prismatic grey aegirine and colorless pectolite 4.2 0.3 2.091 2.088 0 3 7 (Figs. 1 and 2). The mineral assemblage probably 27.1 23.7 2.057 2.055 1 4 5 formed as a result of a hydrothermal event. Conditions 13.5 4.9 1.982 1.984 4 0 0 during metamorphism were in the range of 270–420 8C 5.9 6.2 1.937 1.938 4 0 2 at 0.2–1.0 kbar (Kleyenstuber 1984, Gutzmer & 17.8 14.7 1.853 1.856 3 0 7 Beukes 1996). Detailed reviews of the geology and 14.7 7.9 1.818 1.819 4 0 4 mineralogy of the Kalahari Manganese Fields have 8.4 14.8 1.798 1.799 1 4 7 been given by Kleyenstuber (1984), Von Bezing et al. 24.8 25.0 1.778 1.779 3 4 3 (1991), and Gutzmer & Beukes (1996). 17.8 12.6 1.749 1.749 3 2 7 Meieranite crystals in aggregates are granular, up 4.6 6.3 1.721 1.722 0 2 10 5.4 1.8 1.677 1.676 1 6 2 to 0.5 3 0.5 3 0.4 mm in size. No twinning is observed 5.3 7.4 1.657 1.657 2 0 10 macroscopically.
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