[pharrington]

Quarks are charged, and thus interact with photons. If reacting with photons is not what you meant by "Given that you'll never see a lone quark", but instead you mean something like, for example, `a single one can be formed as a first order byproduct of a physical interaction`, there is no coherent definition of matter that I am aware of where atoms are the smallest unit, but photons or electrons are not.

edited: updated for precision