Q: At what point is a stone no longer “natural stone”? We’re working with more and more slabs that have backers and fillers and resined faces. It seems as if we no longer have the right to call them “natural.” Where do we draw the line here?

A: There probably isn’t going to be a consensus on this, although I know where I draw the line in defining “natural stone.” At StonExpo, and possibly a few other venues during a typical year, I teach a basic class covering rudimentary information on stone types, formation, mineralogy, properties and definitions.

The class can serve as either an informative primer for those relatively new to the industry, or it can serve as a sure cure for insomnia, depending on the student. At the start of that class, I offer a definition of natural stone as: “Stones which have been harvested from their in-situ position in the earth, then cut and machined into final products without alteration to the internal fabric of the material.” 

The distinction for me is that even though a filler has been used or a resin has been used, the voids that are occupied by those materials are natural voids and have always existed within the stone fabric. We’ve been filling voids in travertine forever, and no one has ever said that it made the product “unnatural.” The mineral distribution in the stone, whether filled, mesh-backed or resined, is exactly as nature created it. Any two adjacent minerals in that stone are still in the same position relative to each other that they were a billion or more years ago.

- Chuck Muehlbauer, Marble Institute of America