how to describe the set of acceptable clay-like substances.
Given the context, I would have hoped something involving a mass spectrometer or something similar rather than buying something purely on the basis that it is known to have the property of being suitable for cats to urinate into and then hoping that they don't ever change the mixture on any products in the range.
I bet the thinking was something along the lines of "kitty litter is an inert absorptive material", and nobody really thought much about the differences between types of kitty litter, and whether or not they were truly inert.
Given the context, I would have hoped something involving a mass spectrometer or something similar rather than buying something purely on the basis that it is known to have the property of being suitable for cats to urinate into and then hoping that they don't ever change the mixture on any products in the range.