[Lonesome in Massachussets]

http://blogs.reuters.com/felix-salmon/2012/03/25/the-problem-of-fake-gold-bars/

Gold is far more conductive than tungsten and slightly denser.

X-ray crystallography requires making a powder of the sample, it is not non-destructive in the sense that the sample cannot retain its form.

[Revel]

So just connect some voltage to the Bar and see if it lights up....LOL