It might be useful to have spheres of some of the precious metals (silver, gold, etc.) next to the water sphere to help set the frame of reference. I'm guessing they'll be much, much smaller than the water sphere.
The actual amount of gold in the Earth is pretty poorly constrained, because most of it is expected to be at the core.
The actual amount of gold in the Earth is pretty poorly constrained, because most of it is expected to be at the core.
edit: I found an estimate (http://discovermagazine.com/2006/sep/innerfortknox) of 1.6e15 tons of gold in the Earth's core. The Earth's oceans, for comparison, have a mass of about 1e18 tons.