Ordering of calcium and vacancies in calcium catapleiite CaZr[Si3O9] • 2H2O

The role of local heteropolyhedral substitutions in the stoichiometry, topological characteristics and ion-migration paths in the eudialyte-related structures: a quantitative analysis

“…titano-and niobosilicates) that frequently contain subunits of corner-or edge-sharing M-centered polyhedra, Zrcentered polyhedra in zirconosilicates are usually isolated from each other. Most microporous zirconosilicate structures possess large cages and channels, resulting in interesting ionexchange properties of respective materials (Pekov et al, 2010;Zubkova et al, 2007Zubkova et al, , 2020Zubkova et al, , 2019Fewox et al, 2011;Coleman et al, 2010;Ferreira et al, 2010;Mesto et al, 2014;Chukanov et al, 2010;Aksenov et al, 2016;Zubkova & Pushcharovsky, 2008). Despite the presence of large N(1)-N(5) cages, ionexchange properties of the EGMs have never been experimentally confirmed (Chukanov et al, 2004;.…”

Plumbogaidonnayite, PbZrSi3O9⋅2H2O, a new Pb-member of the gaidonnayite group from the Saima alkaline complex, Liaoning Province, China

“…Ion exchange occurs widely in gaidonnayite-group minerals and similar zirconosilicates (e.g. catapleiite- and hilairite-group minerals) under natural and experimental conditions (Pushcharovskii et al ., 2002; Aksenov et al ., 2016; Celestian et al ., 2019). Recent experimental work has demonstrated that Cs + could exchange at the extra-framework cation (Na) site into the gaidonnayite structure from room temperature to 95°C (Celestian et al ., 2019), which implies that plumbogaidonnayite could crystallise from eudialyte alteration or its alteration product (e.g.…”

“…gaidonnayite and georgechaoite) in a naturally lowtemperature fluid environment. In comparison with isovalent substitution, heterovalent ion exchange in isomorphism would not only influence the main Raman vibrational features and unit-cell parameters, but also tends to cause more vacancies at the extra-framework cation sites and decrease the symmetry, as demonstrated by Na + → Ca 2+ exchanges in calciocatapleiite and calciohilairite, Na + → Zn 2+ exchanges in vigrishinite and zvyaginite, and Na + → Pb 2+ exchange in plumbogaidonnayite (Pushcharovskii et al, 2002;Pekov et al, 2013Pekov et al, , 2014Aksenov et al, 2016). However, although Ca occupies the Na1 site over other cations (except vacancies) during our plumbogaidonnayite structure refinement, the Ca member of gaidonnayite has never been discovered in natural samples, probably due to compositional similarity to calciocatapleiite (Mandarino and Sturman, 1978;Ilyushin et al, 1981).…”