Abstract

Hyttsjoite, circa Pb18Ba2Ca5Mn22+Fe23+Si30O90Cl · 6H2O, is a new mineral from the Lång-ban mines, Filipstad district, Varmland, Sweden. It occurs sparingly in Mn-rich skam with andradite, hedyphane, aegirine, rhodonite, melanotekite, calcite, quartz, potassium feldspar, pectolite, and barite. It is inferred to have formed below 300 °C at 2-4 kbar from the breakdown of medium-temperature metamorphic assemblages in which hedyphane was the principal reactant. The name is from Hyttsjön, which is a lake situated west of the Långban mines. The average analysis is SiO2 26.38, Al2O3 0.02, Fe2O3 2.77, CaO 4.35, MnO 2.00, PbO 58.13, BaO 4.65, Cl 0.65, H2O (calc) 1.58, O = Cl -0.15, total 100.40 wt%. Hyttsjoite grains are mostly 0.1-0.6 mm across, subequant to skeletal in outline, and colorless, and they have a prominent {001} cleavage. Optically, the mineral is uniaxial (–), ω = 1.845(4), ε ≈ 1.815. It is trigonal, space group R3, a = 9.865(2), c = 79.45(1) Å, V = 6695(3) Å3, and Z = 3; Dcalc = 5.10 g/cm3. The most intense X-ray (Fe λ = 1.9373 Å) powder diffraction lines are as follows [d(Å){I)(hkl)]. 13.4(50)(006), 4.43(30)(0.0.18), 3.98(30)(027,1.1.12), 3.32(100)(1.0.22,0.0.24,1.1.18), 3.11 (40)(217,128), 2.969(40)(2.1.10,0.2.19,1.0.25,1.2.11,0.0.27), and 2.671(80)(1.0.28,2.0.23,1.2.17). The crystal structure consists of composite SiO4 + PbOn layers of two kinds (L1 and L2), which are supported by column segments parallel to c, the columns being composed of face-sharing CaO9, FeO6, BaO12, and MnO6 polyhedra. Each layer has two sheets of SiO4 tetrahedra in pin wheel-like modules, joined together to form a puckered planar network filled out by PbOn groups. Layer L1 is continuous (Si8O23), with intralayer Mn, whereas L2 is discontinuous (Si7O22), with intralayer Fe and Ca. L1 and L2 are distinct from layers in other layered silicates, although they show some similarities to layers in minerals of the gyrolite group.

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