Wastes accumulated at Piekary Śląskie, Poland, are the result of 150 years of continuous working of the Orzeł Biały smelting plant. Slags are composed of: oxides (spinel, hematite, zincite); silicates and aluminosilicates (olivine, monticellite–kirschteinite, titanite, merwinite, pyroxene, melilite, feldspars: plagioclases and plumbean K-feldspar, nepheline, kalsilite, leucite); sulfides (pyrrhotite, rudashevskyite, galena), metallic phases (pure iron and iron–arsenic mixture) and secondary phases (gypsum, rapidcreekite, apatite). Interstices between the crystalline phases are filled by glass, concentrating toxic and potentially harmful elements, e.g. up to 53.22 wt.% PbO. The sequence of crystallization of primary phases depended on the local variability of oxygen fugacity and degree of calcination, while the texture type resulted from the cooling time and partial pressure of volatiles. Suggested crystallization temperatures are in the range of 1200–1500°C. Bulk chemical analyses show that the slags are composed mainly of SiO2, Al2O3,Fe2O3, MgO and CaO. Among the potentially harmful elements, Zn is the most common, reaching up to 5.93 wt.%, Pb is present in concentrations up to 3.9 wt.% and As in weathered samples exceeds 1 wt.%. Leaching tests of these elements confirms As mobility as Zn and Pb are preferably leached from fresh slags, while As is present in greater amounts in leachate from weathered slag samples. The documented amounts of As, Zn, Pb and their mobility in slags produce an environmental risk, as this material is currently used widely for commercial purposes.

The name 'tobermorites' includes a number of calcium silicate hydrate (C-S-H) phases differing in their hydration state and sub-cell symmetry. Based on their basal spacing, closely related to the degree of hydration, 14, 11 and 9 Å compounds have been described. In this paper a new nomenclature scheme for these mineral species is reported. The tobermorite supergroup is defined. It is formed by the tobermorite group and the unclassified minerals plombièrite, clinotobermorite and riversideite. Plombièrite ('14 Å tobermorite') is redefined as a crystalline mineral having chemical composition Ca5Si6O16(OH)2·7H2O. Its type locality is Crestmore, Riverside County, California, USA. The tobermorite group consists of species having a basal spacing of ∼11 Å and an orthorhombic sub-cell symmetry. Its general formula is Ca4+x(AlySi6–y)O15+2x–y·5H2O. Its endmember compositions correspond to tobermorite Ca5Si6O17·5H2O (x = 1 and y = 0) and the new species kenotobermorite, Ca4Si6O15(OH)2·5H2O (x = 0 and y = 0). The type locality of kenotobermorite is the N'Chwaning II mine, Kalahari Manganese Field, South Africa. Within the tobermorite group, tobermorite and kenotobermorite form a complete solid solution. Al-rich samples do not warrant a new name, because Al can only achieve a maximum content of 1/6 of the tetrahedral sites (y = 1). Clinotobermorite, Ca5Si6O17·5H2O, is a dimorph of tobermorite having a monoclinic sub-cell symmetry. Finally, the compound with a ∼9 Å basal spacing is known as riversideite. Its natural occurrence is not demonstrated unequivocally and its status should be considered as “questionable”. The chemical composition of its synthetic counterpart, obtained through partial dehydration of tobermorite, is Ca5Si6O16(OH)2. All these mineral species present an order-disorder character and several polytypes are known. This report has been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification.

Selective precipitation of schwertmannite was identified in the water column of a chemically stratified acidic lake (pH 2.0 2.5). A set of analytical techniques was used to identify accurately the mineral phase (X-ray diffraction, X-ray fluorescence spectrometry, scanning electron microscopy coupled with energy dispersive spectroscopy). The lake has two clearly differentiated layers: a thin superficial layer that extends to ∼2 m in depth with less dissolved solid content and, therefore, lower density, which contrasts with a thicker lower layer that extends to 34 m in depth. The upper layer is strongly influenced by climatic factors, triggering dilution (rainfall), concentration (dry season) and intense seasonal thermal fluctuations, while the lower layer is more compositionally and thermally stable.

Schwertmannite precipitate was initially observed only in the upper layer, adhered to a plastic buoy and the anchor line. The latter was confirmed through a test involving a precipitation device that consisted of maintaining a series of plastic plates at different depths over a period of several months. Only the plates located in the upper layer became covered with precipitate, whereas the plates that were submerged in the lower layer remained clean. These observations clearly differed from the saturation indices of schwertmannite (SIsch) calculated using PHREEQC and using Bigham et al. (1996) or Kawano and Tomita (2001) solubility products. Schwertmannite would not precipitate in the lake with the former but would precipitate in both layers with the latter. It is the constant provided by Yu et al. (1999) that makes SIsch in both layers approach the observed behaviour: SIsch>0 displays oversaturation in the upper layer while SIsch<0 displays undersaturation in the lower layer. The value of the product of solubility that better adjusts to this situation is log Ksch = 9.5 10. Using the method by Yu et al. (1999) to establish the apparent solubility, a range of log Ksch values was defined between 10.5 and 11.5 for the system studied.