Original paper
Cyprine, Ca19 Cu2+ (Al, Mg, Mn)12 Si18 O69 (OH)9, a new vesuvianite-group mineral from the Wessels mine, South Africa
Panikorovskii, Taras L.; Shilovskikh, Vladimir V.; Avdontseva, Evgenia Yu.; Zolotarev, Andrey A.; Pekov, Igor V.; Britvin, Sergey N.; Hålenius, Ulf; Krivovichev, Sergey V.
European Journal of Mineralogy Volume 29 Number 2 (2017), p. 295 - 306
published: Apr 1, 2017
Abstract
Cyprine, ideally Ca19 Cu2+ (Al, Mg, Mn)12 Si18 O69 (OH)9, was found at the Wessels mine near Hotazel, Kalahari Manganese 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}, {1 1 0} and {3 3 1}. The Mohs hardness is 6.5. D meas and D calc are 3.40(3) and 3.41 g/cm3, respectively. Cyprine is optically uniaxial, negative, ϖ = 1.744(2), ε = 1.732(2) (in white 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, H2 O by thermogravimetric analysis (TGA)) of two chemically different zones (zone-1/zone-2, wt.%) is: SiO2 36.98/36.51; Al2 O3 14.98/13.70; CaO 36.70/36.18; MgO 3.24/1.10; Mn2 O3 2.27/6.04; CuO 2.39/1.86; Fe2 O3 0.62/2.50; Cr2 O3 0.23/0.04; H2 O 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 Ca18.00 Ca1.00 (Cu0.95 Mg0.05)Σ1.00 Al4.00 (Al5.50 Mg1.00 Mn3+ 1.19 Fe3+ 0.22Cr 0.09) S8.00 ([SiO4]9.91 [H4 O4]0.09) Σ10.00 [Si2 O7]4 ((OH)9 O)Σ10.00 and Ca18.00 Ca1.00 (Cu0.90 Mg0.10)Σ1.00 (Al3.22 Mn3+ 0.60 Fe3+ 0.18)Σ4.00 (Al4.72 Mn3+ 1.20Fe3+ 1.06Mn2+ 0.60Mg0.40Cr0.02) Σ8.00([SiO4] 9.91[H4O4]0.09)Σ10.00 [Si2 O7 ]4 ((OH)9 O)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, 3640 cm-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 – 5.89–0 0 2, 12 – 3.007 – 4 3 1, 47 – 2.950 – 0 0 4, 100 – 2.75 – 4 3 2, 76 – 2.594 – 5 2 2, 35 –2.459–6 2 0, 10–2.324– 1 4 4, 28–1.6224–6 7 2. 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 has been refined to R 1 = 0.034 and R 1 = 0.035 for 2848 and 2071 unique observed reflections with | Fo |≥ 4σF for the zones 1 and 2, respectively. The structure refinements provide scattering factors of the Y 1A, B sites close to 29 e, which supports occupancy of these sites by Cu2+ ions. The copper coordination polyhedra possess strong Jahn– Teller distortion: Y 1A– O6(4 ) = 2.043(3) Å and Y 1A–O10 = 2.258(6) Å for zone-1 and Y 1B– O6(4 ) = 2.010(4) Å and Y 1B–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 Y 1 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.
Keywords
vesuvianite • crystal structure • cyprine • tga/dsc • new mineral • berzelius • copper • south africa • wessels mine • ir • optical spectra