Minerals as Materials – Silicate Sheets Based on Mixed Rings as Modules to Build Heteropolyhedral Microporous Frameworks

In general, a material is classified as porous if its crystal structure is crossed by channels with a free aperture (effective channel width=ecw) at least 3.2A wide, such that the nitrogen molecule, N2, can pass through. In oxysalts, the ecw is calculated by subtracting the ionic diameter of O2− (2.8A) to the O…O distances across the channel (McCusker et al. 2003).