You are right on, Clay's seem cold to the touch vs glass marbles but so do the Polymers imho.
I have not weighed them one vs the other but--I would think that clays are heavier.
Yours appear to have a fingermark or indentation from the hand-rolling process, the Polymer makers that I know of are much more refined than this.
I will settle on clay on these two--who knows really?
@akronmarbles may have an ID and I will defer to him here.
Brian is a collector of the Clays from the USA--he knows way more than I do regarding these.
Marble--On!!