Further on the Choice of Space Group for Scapolite Group Members and Genetic Considerations about the Si-Al Ordering in Their Framework Construction

This paper poses a major question regarding the choice of space group for scapolite mineral group members. An artificial boundary is typically drawn between space groups I4/m and P42/n when solving the structures of scapolites within the marialite–meionite series. The authors debate if solving the crystal structure in lower symmetries is justified. The choice of space group here is attributed to Si-Al ordering of the framework, and it is shown that the interstitial framework cations and anions have an accompanying role in that decision. Some answers on the ranges and limits of distribution of space groups of scapolite members in the marialite–meionite series, and the manifestations of violation of the Lowenstein rule or the so-called aluminum avoidance rule are presented. Modern physical methods (SEM-EDS and SXDA) are employed in the study to properly analyze the solid solution series in detail. New crystal–chemical data are reported for scapolite samples from different localities. An analysis was made for the types of possible Al-O-Al bonds that can occur in the structures at different Al:Si ratios and their influence on Al-Si ordering. Finally, genetic considerations about Al-Si ordering in the framework construction during the mineral formation processes are proposed

Rietveld Analysis of Elpidite Framework Flexibility Using in Situ Powder XRD Data of Thermally Treated Samples

The present study demonstrates the capabilities of the Rietveld procedure to track the structural transformations and framework flexibility on the example of the natural water-containing zirconosilicate elpidite, subjected (in bulk) to thermal treatment from room temperature to 300 °C. The methodological approach to the performed refinements and the obtained results are in accordance with the previously reported data from in situ single crystal X-ray diffraction studies on heated samples of the same mineral. More light has been drawn on the temperature interval in which the non-reconstructive topotactic phase transition occurs upon partial dehydration. The framework flexibility observed as a response to the water loss and subsequent thermal expansion was evaluated in terms of intentionally introduced set of geometric parameters characterizing the spatial orientation of symmetrically related zirconium octahedra in the structure, the coordination polyhedra volumes, their distortion indices, and bond angle variances

Crystal-Chemical and Thermal Properties of Decorative Cement Composites

The advanced tendencies in building materials development are related to the design of cement composites with a reduced amount of Portland cement, contributing to reduced CO2 emissions, sustainable development of used non-renewal raw materials, and decreased energy consumption. This work deals with water cured for 28 and 120 days cement composites: Sample A—reference (white Portland cement + sand + water); Sample B—white Portland cement + marble powder + water; and Sample C white Portland cement + marble powder + polycarboxylate-based water reducer + water. By powder X-ray diffraction and FTIR spectroscopy, the redistribution of CO32−, SO42−, SiO44−, AlO45−, and OH− (as O-H bond in structural OH− anions and O-H bond belonging to crystal bonded water molecules) from raw minerals to newly formed minerals have been studied, and the scheme of samples hydration has been defined. By thermal analysis, the ranges of the sample’s decomposition mechanisms were distinct: dehydration, dehydroxylation, decarbonation, and desulphuration. Using mass spectroscopic analysis of evolving gases during thermal analysis, the reaction mechanism of samples thermal decomposition has been determined. These results have both practical (architecture and construction) and fundamental (study of archaeological artifacts as ancient mortars) applications