Mn-rich norsethite from the Kremikovtsi ore deposit, Bulgaria
Zidarov, Nikola; Petrov, Ognyan; Tarassov, Mihail; Damyanov, Zhelyazko; Tarassova, Eugenia; Petkova, Vilma; Kalvachev, Yuri; Zlatev, Zlati
published: Oct 1, 2009
ArtNo. ESP154018603006, Price: 29.00 €
Mn-rich norsethite, Ba(Mg, Mn)(CO3)2, is described for the first time in Bulgaria, in the Kremikovtsi ore deposit, Sofia district. The mineral occurs as pale-yellow small clusters of platy crystals and spherulites grown upon fine crusts of spheroid siderite crystals in small cavities among granular hydrothermal siderite. Its refraction indices are: nω = 1.698 and nε = 1.527. Electron microprobe analysis reveals in the mineral (in wt. %) BaO 52.8-53.3 (53.1 - average content), MgO 10.2-12.1 (11.3), MnO 3.4-5.7 (4.7) and sporadic quantities of FeO that corresponds well to the averaged formula Ba1.0(Mg0.8Mn0.2)1.0(CO3)2. Powder X-ray diffraction study shows that the studied Mn-rich norsethite is trigonal, space group R3m with slightly larger unit cell parameters than those of the norsethite - a = 5.0318(11) Å, c = 16.8705(15) Å, V = 369.01(3) Å3, z = 3. The strongest observed reflections in the powder diffraction pattern are (d in Å, I observed): 5.629, 38; 3.871, 28; 3.026, 100; 2.109, 25; 1.897, 29; 1.875, 30. The principle absorption bands related to [CO3]2- groups in the IR spectrum are ν1 - 1114 cm-1, ν2 - 880 cm-1, ν3 - 1452 cm-1, and ν4 - 696 cm-1. The DTA-DTG-TG analyses display endothermic effects in 556-776 °C, 820-940 °C and 930-1100 °C temperature regions The observed mineral association and textures suggest interaction of an earlier formed siderite and barite aggregates with hydrothermal solutions and deposition of Mn-rich norsethite and Ca-Mn-Fe bearing norsethite varieties in voids within the hydrothermal siderite.