Why are framework minerals often more compressible than minerals with edge-sharing polyhedrons?

Framework minerals are often more compressible than minerals with edge-sharing polyhedrons because of the specific mechanisms involved in their structural response to pressure.

In framework structures, such as quartz or feldspar, atomic polyhedrons are linked at their corners to form a three-dimensional network. Significant compression in these materials occurs primarily through the bending of metal-oxygen-metal bond angles between the polyhedrons. This bending leads to a collapse of the interpolyhedral spaces, a process that results in a volume change typically an order of magnitude greater than that caused by bond-length changes alone.1

In contrast, minerals characterized by edge- or face-sharing polyhedrons lack these open, flexible networks. Their compression is attributable predominantly to the shortening of interatomic distances (bond compression), which is a much less efficient mechanism for volume reduction than the angular bending found in framework structures.1