Qatranaite, CaZn₂(OH)₆·2H₂O: A new mineral from altered pyrometamorphic rocks of the Hatrurim Complex, Daba-Siwaqa, Jordan

The new mineral qatranaite, CaZn₂(OH)₆·2H₂O(P2₁/c, Z =2,a = 6.3889(8) Å, b = 10.9692(14) Å, c = 5.7588(8) Å; β = 101.949(14)°, V = 394.84(9) ų; IMA2016-024), was found in cuspidine veins cutting spurrite marble in part of the pyrometamorphic Hatrurim Complex located in the Siwaqa region, Jordan. Qatranaite is the natural counterpart of synthetic calcium hexahydroxodizincate dihydrate. It forms colourless or white crystals up to 0.3 mm in size. Qatranaite is associated with cuspidine, sphalerite, Se-bearing thaumasite, afwillite, calcite, srebrodolskite–brownmillerite, spinel–magnesioferrite, spurrite and fluorapatite– fluorellestadite. The new mineral has an irregular fracture; no cleavage or parting were observed. The calculated density of qatranaite is 2.598 g cm³, the microhardness VHN₂₅ = 171 kg mm^-2 corresponds to ~3.5 in the Mohs’ hardness scale. The qatranaite structure is formed by hydroxylated pyroxene-like chains [Zn₂(OH)₆]^2-, between which the [Ca(OH₂)₂]²⁺ groups are located. The Ca atoms are eight-fold coordinated in [Ca(OH)₄(OH₂)₂] polyhedra which share the four hydroxyl oxygen atoms with the Zn-centred tetrahedra. The main bands in the Raman spectrum of qatranaite are related to vibrations in Zn(OH)²4 tetrahedra (cm^-1): 297, 344 (v₂ + v₄); 440, 449, 479 (v₁ + v₃); 990 (vZn–O–Zn); 1065 (vZn–OH). Strong bands at 3190, 3497 and 3624 cm^-1 are assigned to OH stretching vibrations. The strongest diffraction lines are [d_hkl,Å(I)]: 6.25 (33), 5.002 (14), 3.992 (23), 3.124 (47), 2.881 (100), 2.723 (28), 2.451 (12), 1.575 (20). Qatranaite crystallization was preceded by a high-temperature alteration of spurrite rocks, reflected in the formation of cuspidine along fractures. The formation of qatranaite-bearing veins resulted from low-temperature (<70 °C) rock alteration by hyper-alkaline solutions.