Composition, Thermal Expansion and Phase Transitions in Framework Silicates: Revisitation and Review of Natural and Synthetic Analogues of Nepheline-, Feldspar- and Leucite-Mineral Groups

Abstract

Framework silicates form about 70% of the Earth’s crust, mainly feldspars ~50–60% and quartz ~10–15%. Less-abundant feldspathoids include nepheline-, leucite-, and sodalite-group minerals, rich in structurally challenging properties. This review paper deals with anhydrous feldspar-, nepheline-, and leucite/pollucite groups, emphasising the importance of parallel studies on natural and synthetic samples. Four topics are covered. For decades, petrologists have analysed nephelines and recalculated their compositions as endmember molecules but, by not following rules of stuffed-tridymite crystal chemistry, have not estimated reliably the excess SiO2 present in solid solution. Some materials scientists make similar mistakes, and a new approach is described here. Synthesis studies of analogue feldspars, nephelines, and leucite/pollucites led to collaborative studies, mainly using laboratory and synchrotron X-ray powder diffraction methods at room and elevated temperatures, to study thermal expansion and displacive phase transitions. Such work was recently expanded to address the spontaneous strain relations. Topics covered here include work on nepheline/kalsilite analogues in the system SrAl2O4—BaAl2O4; thermal expansion of (K,Na)Al-, RbAl-, RbGa-, and SrAl-feldspars; and thermal expansion and phase transitions in analogue leucites KGaSi2O6 (tetragonal to cubic) and K2MgSi5O12 (monoclinic to orthorhombic). Results are reviewed in the context of research published in mineralogical and more-widely in physical sciences journals.

Mesityl Oxide Reduction by Using Acid-Modified Phonolite Supported NiW, NiMo, and CoMo Catalysts

“…The XRD diagrams (Figure 1) were similar for all solids (i.e., the signals had the same angle). However, the XRD patterns for the Ph-HCl material showed more intense signals related to the feldspar group minerals (sanidine, analcime, and nepheline) [19]. In the case of the materials containing Ni, no clear evidence of NiO crystal phase was found.…”

Monoclinic–orthorhombic first-order phase transition in K2ZnSi5O12 leucite analogue; transition mechanism and spontaneous strain analysis

“…Note that the cell parameter ‘strains’ calculated will reflect errors involved in the estimation of x 0 values with the largest errors occurring at the temperatures furthest from the phase transition. The a 0 , b 0 , c 0 and V 0 values for KMg-Lc were obtained in a similar way from the parameters reported in Table 1 (Redfern and Henderson, 1996); Henderson (2021) has already made a preliminary study of the spontaneous strains for the KMg-Lc data in a review of composition, thermal expansion and phase transitions in framework silicates.

Fig.

…”

“…We have already predicted that P 2 1 / c KZn-Lc should show a phase transition to Pbca at ~700 K (Bell and Henderson, 2018), but the high-temperature data for KZn-Lc reported here show the phase transition occurring over the temperature range 848–863 K where both monoclinic and orthorhombic phases are present. This two phase region is similar to that described for unquenchable, displacive phase transitions shown by kalsilite analogues in the SrAl 2 O 4 –BaAl 2 O 4 system and was named the ‘region of coexistence’ (Henderson and Taylor, 1982); based on similarities shown for displacive phase transitions occurring in ZrO 2 and high-cristobalite, it was suggested that the aluminate ‘nepheline/kalsilite-type’ phase transition had properties of a strain-related martensitic transition (Henderson and Taylor, 1982; Avdeev et al , 2007; Henderson, 2021).…”

“…We have calculated the individual strain parameters from the measured cell parameters for KZn-Lc (this paper) and KMg-Lc (Redfern and Henderson, 1996; see also Henderson, 2021) in an Excel spreadsheet and plot the results in Fig. 6a and b. Note that the values calculated for e 11 , e 22 , e 33 , and V ss have significant uncertainties arising from the need to extrapolate orthorhombic cell parameters over wide temperatures ranges to provide a 0 , b 0 and c 0 for each temperature step in the monoclinic stability field, but e 13 is better constrained because the extrapolated β 0 term is fixed at 90°.…”

Chemical Characterization of Particulate Matter in the Renaissance City of Ferrara

“…In fact, these particles had a chemistry similar to that of leucite, which could testify the reaction of feldspar with the alkaline elements from the organic substance [73]. Therefore, this reaction could probably favor the combustion processes of silica-undersaturated phases [74], which are not present in the natural sediments of the Po Valley.…”