If you take a piece of granite (typically 18"x24" for a TT and at least 3/4" thick) and place it on a bed of sand (typically 3"-4" deep), and add a TT, the combination will way upwards of 30-50 lbs. I guarantee that tapping the granite with a hard object will produce no discernable ring. In fact in my case, such tapping is inaudible through the speakers on quiet passages. I suspect the same it true for bonding the granite with MDF. Try it.
