Modular Microporous Minerals: Cancrinite-Davyne Group and C-S-H Phases

Abstract

In this chapter, we illustrate and discuss two distinct groups of microporous phases: the cancrinite group and the C-S-H compounds of the tobermorite and gyrolite families. The compounds in the fi rst group present a three-dimensional purely tetrahedral framework with, apart from a single exception, Si:Al ratio equal to 1; in the mineralogical classifi cations they are included among feldspathoids and are generally “regarded …… distinct from zeolites, in part, at least, because of the presence of large volatile anions” (Coombs et al. 1998). The members of the second group are characterized by mixed frameworks built up by silicon (and aluminum) tetrahedra and calcium polyhedra. A common feature of both groups is the modular character of their frameworks, which are built up through various stacking ways of a single module (as in the minerals of the cancrinite-davyne family) and two or more modules as in the case of the C-S-H phases

The high-pressure behavior of balliranoite: a cancrinite-group mineral

“…Balliranoite is a rare member of the cancrinite group, which consists of eleven natural species and several synthetic compounds (Bonaccorsi and Merlino 2005;Pekov et al 2011 and references therein), all sharing the [CAN]-topology of the tetrahedral framework (Baerlocher et al 2007) (Figs. 1-3).…”

“…1, 2). All the cancrinite-group minerals, except cancrisilite and tiptopite (Bonaccorsi and Merlino 2005), display a perfectly ordered aluminosilicate framework with compo-sition (Al 6 Si 6 O 24 ). Two subgroups can be defined according to the nature of the extraframework population filling the columns of can units: a) the cancrinite subgroup, where alternated Na-H 2 O clusters give rise to chains of non-equally spaced Na-H 2 O g Na-H 2 O and b) the davyne subgroup, where chains of almost equally spaced Ca-Cl-Ca-Cl occur (Fig.…”

“…Among them, the most common in natural species are CO geometrical constraints on the configuration of the channel population, which can result in an ordering within and between adjacent channels, as occurs in the (SO 2À 4 )-and (Cl À )-end members microsommite (Bonaccorsi et al 2001) and quadridavyne (Bonaccorsi et al 1994), respectively, both showing a superstructure within the (0001) plane (further details are in Bonaccorsi and Merlino 2005). A long-range disorder of the channel population is found in davyne (Bonaccorsi et al 1990;Hassan and Grundy 1990;Bonaccorsi et al 1995;Rozenberg et al 2009), which can be considered as an intermediate member between microsommite and quadridavyne (Bonaccorsi and Merlino 2005). The first evidence of davyne samples having CO 2À 3 as the dominant anionic species (i.e.…”

“…Natural occurrences of cancrinite-group minerals are in alkali-rich and silica-undersaturated environments (Deer et al 2004;Bonaccorsi and Merlino 2005). They can mainly be found in nepheline syenite intrusions as late-stage hydrothermal crystallizations or as replacement products of nepheline and sodalite, and in related volcanic rocks.…”

“…Several synthetic "cancrinites" with highly variable framework and extraframework crystal chemistries have been obtained so far (Bonaccorsi and Merlino 2005;Sirbescu and Jenkins 1999 and references therein). Although stacking faults (insertion of hexagonal layers in a C position) and the concomitant presence of cationic and anionic species within the channel result in a reduced ionic exchange capacity, complete Na ) Li and Na ) Ag exchanges have been reported for synthetic hydroxy-cancrinite (Barrer and Falconer 1956).…”