Search

Stergiouite is a new mineral from the Plaka area in the northern part of the Lavrion Mining District, Greece. The mineral occurs as clusters of stacked, platy crystals, associated with galena, sphalerite, native arsenic and sulfur. The crystals are white to colorless, with a pearly luster and white streak. No luminescence under ultraviolet (UV) radiation is observed. Stergiouite is brittle and has a Mohs hardness of ~3. Chemical analysis gave As2O5 42.93 wt%; Sb2O5 2.45 wt%; CaO 10.90 wt%; ZnO 29.79 wt%; and H2Ocalc 13.93 wt%, which corresponds to an empirical formula Ca1.02Zn1.91((As0.95Sb0.08)O4)Σ2.03 · 4H2O. The ideal formula is CaZn2(AsO4)2 · 4H2O. Stergiouite is monoclinic, space group Pc, with unit-cell parameters a 9.416(2) Å; b 5.300(1) Å; c 10.893(2) Å; β 91.767(10)°; V 543.36(3) Å3; Z = 2. The strongest lines in the Gandolfi X-ray powder pattern [d in Å, I/I100, (hkl)] are: 9.406, 100, (100); 4.619, 80, (102), (110); 3.612, 35, (20 2 ¯ ); 3.494, 35, (112); 2.984, 60, (21 2 ¯ ); 2.922, 50, (212); 2.720, 20, (004); and 2.647, 25, (020). The crystal structure was refined based on single-crystal X-ray diffraction data to R1 = 0.046, wR2 = 0.093. The observed mass density of 3.1(2) g cm−3 compares well with the calculated value (3.183 g cm−3). The framework structure of stergiouite is built up by one type of CaO2(H2O)4 octahedron and each two ZnO4 and AsO4 tetrahedra. These polyhedra share common corners to form three- and four-membered rings. A system of hydrogen bonds (O–O range: 2.70–3.02 Å) further stabilizes the structure. The crystal structure of stergiouite is closely related to that of phosphophyllite [Fe[6]Zn2[4](PO4)2 · 4H2O] as well as with members of the hopeite [Zn[6]Zn2[4](PO4)2 · 4H2O] group. Stergiouite is named in honour of Vasilis Stergiou (born 1958) in recognition of his contributions to the mineralogy of the Lavrion deposits. [ABSTRACT FROM AUTHOR]

The crystal structure (R = 0.0750) of fiedlerite-1A Pb3Cl4F (OH) · H2O from ancient slags of Lavrion (Greece) was studied on a single crystal. The mineral is triclinic, a = 8.5741 (7) Å, b = 8.0480 (5) Å, c = 7.2695 (4) Å, α = 90.087 (5), β = 102.126 (6), γ = 103.424 (6)°, V = 476.37 (6) Å3, Z = 2. The Pb2+ cations center the Pb(1)F(H2O)Cl6, Pb(2)(OH)2FCl5, and Pb(3)(OH)F2Cl5 bicapped trigonal prisms. In the structure there is an additional position Pb', filled by 10% with Pb2+. There are two main structural fragments alternating along the a axis: (100) layers of Pb(2)- and Pb(3)-centred polyhedra and zigzag chains, stretched along the b axis formed by Pb(1)-centred polyhedra sharing common edges. The IR spectrum of fiederlite-1A is given. [ABSTRACT FROM AUTHOR]