Obvious isnt it?? thats shinden skin

ha thats my guess but I have, of course, not seen anywhere near enough to know anything.

I have observed this though it may not be a fair assessment. So Y doesn't say he can tell; nor does he say his Dad can. He says his Dad says he can. meaning maybe he does not quite believe it himself.

You would never know unless you tried to trick him; and even then maybe he would be correct should the stone have been stamped from one mine but actually taken from another