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

Cyprine, ideally Ca₁₉Cu²⁺(Al,Mg,Mn)₁₂Si₁₈O₆₉(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, ω = 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, H₂O by thermogravimetric analysis (TGA)) of two chemically different zones (zone-1/zone-2, wt.%) is: SiO₂ 36.98/36.51; 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 Ca_8.00Ca_1.00(Cu_0.95Mg_0.05)_Ʃ1.00Al_4.00(Al_5.50Mg_1.00Mn³⁺_1.19Fe³⁺_0.22Cr_0.09)_Ʃ8.00([SiO₄]_9.91[H₄O₄]_0.09)_Ʃ10.00[Si₂O₇]₄((OH)₉O)_9.91 and Ca_18.00Ca_1.00(Cu_0.90Mg_0.10)_Ʃ1.00(Al_3.22Mn³⁺_0.60Fe_30.18)_Ʃ4.00(A_l4.72Mn³⁺_1.20Fe³⁺_1.06Mn²⁺_0.60Mg_0.40Cr_0.02)_Ʃ8.00([SiO₄]_9.91[H₄O₄]_0.09)_Ʃ10.00[Si₂O₇]₄((OH)₉O)_Ʃ10.00 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): 12–5.89–002, 12–3.007–431, 47–2.950–004, 100–2.75–432, 76–2.594–522, 35–2.459–620, 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) ų,Z = 2. The crystal structure has been refined to R₁ = 0.034 and R₁ = 0.035 for 2848 and 2071 unique observed reflections with |F_o| ≥ 4σ_F 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 by Cu²⁺ 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.