Zálesíite, a new mineral of the mixite group, from Zálesí, Rychlebské hory Mts., Czech Republic
Sejkora, J.; Řídkošil, T.; Šrein, V.
published: Dec 1, 1999
ArtNo. ESP154017502001, Price: 29.00 €
Zálesíite, CaCu6 [(AsO42 (AsO3OH) (OH)6] x 3 H2O, is hexagonal, with space group P 63/m inferred from isotypic agardite - (Y) and mixite, and with a = 13.571 (1) Å, c = 5.880(1) Å, V = 937.8(2) Å3, Z = 2, Dcalc. = 3.50 and Dmeas. = 3.49(2) g/cm3. The strongest lines in XRD pattern are (d in Å/I/Io (hkl)): 11.64/100 (100), 4.431/41 (111, 210), 2.935/42 (221, 400), 2.693/29 (112, 320, 230), 2.562/30 (140). Zálesííte forms transparent minute acicular crystals up to 0.1 mm in length and in 10 µm, in width, which produce crystalline hair-like coatings up to 1 cm2 on quartz gangue, cross-fiber veinlets and filling of small (up to 5 mm) cavities of gangue. It has a pale green color, white streaks, vitreous lustre; Mohs' hardness is about 2-3. No fluorescence at 254 and 366 nm of UV light was observed. Zálesíite is uniaxial positive, with refraction indices ω = 1,688 (2) and ɛ = 1,765 (2) at Na light (589 nm) and dichroic: pale yellow green (O) - pale green (E) with ɛ > ω. Chemical analysis yields an average composition of CaO 5.46, CuO 46.46, Y2O3 1.50, Al2O3 0.26, La2O3 0.10, AS2O5 34.27, P2O5 0.37, H2O 11.95, total 100.37 wt. %, leading to a formula CaCu6 [(AsO4) (AsO3OH) (OH)6] x 3 H2O. Zálesíite originated by weathering of chalcopyrite and cobalt arsenides in conditions of supergene zone in-situ. Zálesíite was found in association with chalcopyrite, chrysocolla, clinoclase, conichalcite, erythrite, malachite, metanovacekite, metatorbernite, novacekite, quartz, tyrolite, uranophane and zeunerite. The name is for the locality Zálesí. Zálesíite is compared with other minerals of the mixite group, and its X-ray powder diffraction data, thermal analysis and infrared spectra are given.