Babánekite, Cu3(AsO4)2 ∙ 8H2O, from Jáchymov, Czech Republic - a new member of the vivianite group

Abstract

Babánekite, Cu 3 (AsO 4 ) 2 •8H 2 O, a new member of the vivianite group was found in material originating from the Geister vein, Rovnost mine, Jáchymov, Western Bohemia, Czech Republic. It occurs as a supergene alteration mineral in association with members of the lindackerite supergroup (veselovskýite, hloušekite, pradetite and lindackerite), lavendulan, gypsum and an X-ray amorphous Cu-Al-Si-O-H phase. Crystals of babánekite are pinkish to peach-colored, elongated, prismatic and up to 2 mm in length. They exhibit the forms {010}, {100}, {110}, {101} and less frequently also {001}. Crystals are transparent to translucent with a vitreous luster. The mineral has a light pinkish streak. Estimated Mohs hardness is between 1.5 and 2. The cleavage is perfect on {010}.

Horákite, a new hydrated bismuth uranyl-arsenate-phosphate mineral from Jáchymov (Czech Republic) with a unique uranyl-anion topology

“…This association is typical of the Geister vein in the Rovnost mine (see, e.g. Plášil et al 2017). The new mineral is of supergene origin, having formed in-situ in the oxidation zone.…”

Monteneroite, Cu2+Mn2+2(AsO4)2⋅8H2O, a new vivianite-structure mineral with ordered cations from the Monte Nero mine, Liguria, Italy

“…The coordinations of the M1 and M2 sites, while both octahedral, are significantly different. Several investigations for Mg-bearing vivianite-structure-type phases have shown partial ordering of cations between the M1 and M2 sites and, as noted above, barićite was shown by Yakubovich et al (2001) to have Fe dominant in the M1 site and Mg dominant in the M2 site; however, for those phases in which the principal cations are Co, Zn, Ni or Cu, site ordering has not been conclusively shown, possibly because of the similarities in scattering powers of these cations (see Plášil et al, 2017, and references therein).…”

“…Besides the strong ordering of Cu and Mn indicated by the refinement, the ordering is also supported by bond-valences summations (BVS) at these sites. The M1 site has a BVS of Monteneroite is an ordered intermediate between manganohörnesite (Gabrielson, 1954), Mn 2+ 3 (AsO 4 ) 2 •8H 2 O, and babánekite (Plášil et al, 2017), Cu 2+ 3 (AsO 4 ) 2 •8H 2 O.…”

“…Monteneroite is an ordered intermediate between manganohörnesite (Gabrielson, 1954), Mn 2+ 3 (AsO 4 ) 2 ⋅8H 2 O and babánekite (Plášil et al , 2017), Cu 2+ 3 (AsO 4 ) 2 ⋅8H 2 O. Selected data for arsenate minerals with the vivianite structure are compared in Table 7.…”

“…Until now, all minerals and synthetic vivianite-type phases, except barićite, have exhibited dominance of the same cation in the M 1 and M 2 sites, although partial ordering has been documented in some cases. The reader is referred to the detailed discussion of this subject in the descriptive paper on babánekite, Cu 3 (AsO 4 ) 2 ⋅8H 2 O, by Plášil et al (2017). Note that Yakubovich et al (2001) showed Fe to be dominant in the M 1 site and Mg to be dominant in the M 2 site in barićite; however, the mineral has never been formally redefined to reflect this and it is still regarded as the Mg-dominant analogue of vivianite with the formula (Mg,Fe) 3 (PO 4 ) 2 ⋅8H 2 O.…”