Hrabákite, Ni₉PbSbS₈, a new member of the hauchecornite group from Příbram, Czech Republic

Abstract

The new mineral hrabákite (IMA2020-034) was found in siderite–sphalerite gangue with minor dolomite–ankerite at the dump of shaft No. 9, one of the mines in the abandoned Příbram uranium and base-metal district, central Bohemia, Czech Republic. Hrabákite is associated with Pb-rich tučekite, Hg-rich silver, stephanite, nickeline, millerite, gersdorffite, sphalerite and galena. The new mineral occurs as rare prismatic crystals up to 120 μm in size and allotriomorphic grains. Hrabákite is grey with a brownish tint. Mohs hardness is ca. 5–6; the calculated density is 6.37 g.cm–3. In reflected light, hrabákite is grey with a brown hue. Bireflectance is weak and pleochroism was not observed. Anisotropy under crossed polars is very weak (brownish tints) to absent. Internal reflections were not observed. Reflectance values of hrabákite in air (Rmin–Rmax, %) are: 39.6–42.5 at 470 nm, 45.0–47.5 at 546 nm, 46.9–49.2 at 589 nm and 48.9–51.2 at 650 nm). The empirical formula for hrabákite, based on electron-microprobe analyses (n = 11), is (Ni8.91Co0.09Fe0.03)9.03(Pb0.94Hg0.04)0.98(Sb0.91As0.08)0.99S7.99. The ideal formula is Ni9PbSbS8, which requires Ni 47.44, Pb 18.60, Sb 10.93 and S 23.03, total of 100.00 wt.%. Hrabákite is tetragonal, P4/mmm, a = 7.3085(4), c = 5.3969(3) Å, with V = 288.27(3) Å3 and Z = 1. The strongest reflections of the calculated powder X-ray diffraction pattern [d, Å (I)(hkl)] are: 3.6543(57)(200); 3.2685(68)(210); 2.7957(100)(211); 2.3920(87)(112); 2.3112(78)(310); 1.8663(74)(222); and 1.8083(71)(302). According to the single-crystal X-ray diffraction data (Rint = 0.0218), the unit cell of hrabákite is undoubtedly similar to the cell reported for tučekite. The structure contains four metal cation sites, two Sb (Sb1 dominated by Pb2+) and two Ni (with minor Co2+ content) sites. The close similarity in metrics between hrabákite and tučekite is due to similar bond lengths of Pb–S and Sb–S pairs. Hrabákite is named after Josef Hrabák, the former professor of the Příbram Mining College.

Argentopolybasite, Ag16Sb2S11, a new member of the polybasite group

“…% (Kasatkin et al, 2022) with Cu<0.50 apfu. The third case is the first approved Agdominant member (Cu in module layer B fully substituted by Ag) of the polybasite group, the new mineral argentopearceite-T2ac (IMA 2020-049; Sejkora et al, 2020).…”

“…The same limit was approved in the case of pearceite/argentopearceite (IMA 2020-049; Sejkora et al, 2020).…”

“…Argentopolybasite is named in accordance with the existing nomenclature scheme for the polybasite-group minerals (Bindi et al , 2007c). As this new mineral has Sb > As and the structural position ‘Cu’ of the B module layer is dominated by Ag, it has been named argentopolybasite to indicate that it is the Ag-dominant analogue of polybasite and, at the same time, the Sb-dominant analogue of the recently defined argentopearceite (Sejkora et al , 2020). Moreover, as it exhibits the 221 unit-cell type, the full name for the polytype is argentopolybasite- T 2 ac , the Ag-dominant analogue of polybasite- T 2 ac (Bindi et al , 2007c).…”

Neobvyklá asociace minerálů s willemitem z prostoru centrální části příbramského uran - polymetalického revíru (Česká republika)

“…Pozoruhodné jsou zejména nenulové obsahy smithsonitové složky, zaznamenané ve všech získaných analýzách vyjma tří. Jinak je chemismus kalcitu dobře srovnatelný s dalšími podrobně studovanými lokalitami v rámci příbramského uran -polymetalického revíru (Sejkora et al 2019(Sejkora et al , 2021(Sejkora et al , 2022Dolníček et al subm. ).…”

“…Obsah vápníku kolísá mezi 0.94 a 1.19 apfu; báze přepočtu 2 kationty kovů na vzorcovou jednotku. Společným znakem všech získaných bodových analýz je systematicky (ve všech získaných analýzách) zvýšený podíl zinku, který v karbonátech dolomitové skupiny z dosud podrobně studovaných lokalit v rámci příbramského uran -polymetalického revíru(Sejkora et al 2021(Sejkora et al , 2022Dolníček et al subm. ) nebyl zjištěn.…”