Check out some of the figures for density (weight/volume, not the other kind of density) of various qualities of granite: http://www.gemgranites.com/html/index2.htm
Looking at some of those figures, the comparative size of the stone - while it sounds impressive - is probably around 1.5 cubic meters in size.
Like undercover said, this isn't going to prove to anyone how evil the WTS - the corporation - is, nor is it going to make local JWs look materialistic. If anything it helps them look more mainstream.