Cyprine, Ca19Cu2+(Al,Mg,Mn)12Si18O69(OH)9, a new vesuvianite-group mineral from the Wessels mine, South Africa

Taras L. Panikorovskii, Vladimir V. Shilovskikh, Evgenia Yu Avdontseva, Andrey A. Zolotarev, Igor V. Pekov, Sergey N. Britvin, Ulf Hålenius, Sergey V. Krivovichev

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Abstract

Cyprine, ideallyCa19Cu2+(Al,Mg,Mn)12Si18O69(OH)9,was found at theWessels mine near Hotazel,KalahariManganese Field, North Cape province, South Africa. It occurs as chaotic aggregates (up to 5 cm across) in open cavities or embedded in coarse-grained colourless calcite. Associated minerals are calcite, apatite, andradite, henritermierite and rhodochrosite. Single crystals of cyprine up to 1 cm are dark red with a lilac hue and vitreous lustre.Dominant crystal forms are {1 0 0}, {11 0} and {3 3 1}. TheMohs hardness is 6.5.Dmeas and Dcalc are 3.40(3) and 3.41 g/cm3, respectively. Cyprine is optically uniaxial, negative, ω = 1.744(2), e = 1.732(2) (inwhite light). Pleochroism is strong; ranging from O= dark purple, E= pale red to O= dark reddish brown, E= pale yellowish brown; O>E. Chemical composition (electron microprobe, H2O by thermogravimetric analysis (TGA)) of two chemically different zones (zone-1/zone-2, wt.%) is: SiO236.98/36.51; Al2O3 14.98/13.70; CaO 36.70/36.18; MgO 3.24/1.10; Mn2O3 2.27/6.04; CuO 2.39/1.86; Fe2O3 0.62/2.50; Cr2O3 0.23/0.04; H2O 3.30/3.30, total 100.71/101.23. The crystal-chemical formulae (based on the FTIR, TGA/differential scanning calorimetry, SREF, WDS and optical spectra) are Ca18.00Ca1.00(Cu0.95Mg0.051.00Al4.00(Al5.50Mg1.00Mn3+ 1.19Fe3+ 0.22Cr0.098.00([SiO4]9.91[H4O4]0.0910.00 [Si2O7]4((OH)9O)Σ10.00 and Ca18.00Ca1.00(Cu0.90Mg0.10)Σ1.00(Al3.22Mn3+ 0.60Fe3+ 0.18)Σ4.00(Al4.72Mn3+ 1.20Fe3+ 1.06Mn2+ 0.60Mg0.40Cr0.02) S8.00([SiO4]9.91[H4O4]0.09)Σ10.00[Si2O7]4((OH)9O)Σ10.00 for zone-1 and zone-2, respectively. Absorption bands in the IR spectrum are 443, 490, 574, 604, 671, 814, 905, 972, 1015, 3354, 3640cm-1. The polarized optical absorption spectra have two strong absorption bands at 415 and 555 nm and a less intense band at 645 nm. The eight strongest lines of the powder X-ray diffraction pattern are (I-d(Å)-h k l): 12-5.89-002, 12-3.007-4 3 1, 47-2.950-004, 100-2.75-4 3 2, 76-2.594-522, 35-2.459-6 2 0, 10-2.324-144, 28-1.6224-672. Cyprine is tetragonal, space group P4/n, unit-cell parameters refined from the powder data are a = 15.5652(5), c = 11.7921(4), V= 2863.2 (2)Å3,Z = 2.The crystal structure hasbeen refined toR1=0.034andR1 = 0.035for2848and2071unique observedreflectionswith |Fo|=4sF for the zones 1 and 2, respectively. The structure refinements provide scattering factors of the Y1A,B sites close to 29 e-, which supports occupancy of these sites byCu2+ ions.The copper coordination polyhedra possess strong Jahn-Teller distortion: Y1A-O6(4-) = 2.043(3)Å and Y1A-O10 = 2.258(6)Å for zone-1 and Y1B-O6(4-)=2.010(4)Å and Y1B-O10 = 2.274(7)Å for zone-2. Cyprine is defined as a member of the vesuvianite group with Cu2+ as a dominant cation in the Y1 site. The historical name cyprine (derived from Latin cuprum, copper) given by J.J. Berzelius in 1821 for Cu-bearing vesuvianite is transferred to the new mineral.

Original languageEnglish
Pages (from-to)295-306
Number of pages12
JournalEuropean Journal of Mineralogy
Volume29
Issue number2
DOIs
Publication statusPublished - 2017

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Scopus subject areas

  • Geochemistry and Petrology

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