Personally, I don not think rock is soft matter.

Because:

Soft matter is a subfield of condensed matter comprising a variety of physical systems that are deformed or structurally altered by thermal or mechanical stress of the magnitude of thermal fluctuations. Soft matter include liquids, colloids, polymers, foams, gels, granular materials, liquid crystals, and a number of biological materials. These materials share an important common feature in that predominant physical behaviors occur at an energy scale comparable with room temperature thermal energy. At these temperatures, quantum aspects are generally unimportant.

cited from https://en.wikipedia.org/wiki/Soft_matter

Typical soft matter encompasses materials that really cannot to classified as either solids or liquids. For example, glue, ketchup, pastes, Jell-O – are they solid or liquid? They  seem to have properties of both. Pierre-Gilles de Gennes, who won the Nobel Prize in physics in 1991 for his work on such materials defined them to be materials on which a mild external influence has a large effect. Typically these are materials that are held together by weak inter-molecular interactions, such as van der Waals forces. Gels such as Jell-O are a common type of soft matter. Gels have a solid phase such as a three-dimensional network of crosslinked (interconnected) filaments interspersed within a liquid. Many of the gels found in biological systems, such as actin networks in cells, are comprised of networks of biological polymers that have both viscous and elastic properties.

cited from http://umdberg.pbworks.com/w/page/70240088/Soft%20matter%20%282013%29