The picture here is from a 2015 show. You can see behind the table the yellow rope and cinderblock weight I use to anchor the tent. The top features ionic sowbelley agate slabs from mines near Creede Colorado. They are formed when hot water leaching through the rocks deposits some minerals in the rock. The minerals here look wonderful. Not too far from where this rock was found the minerals deposited were gold and silver! There might be a trace of them in these slabs, but not enough to make extracting it practical.
I got several sowbelley agate slabs from my cousin's rockshop. My wife told me I had to use 1, 3, or 5 to make a pleasing pattern. The Whilpool design is what I came up with. I've since found that I can make pleasing desings with sets of 2 or 4 focus stones too. In fact I have a specatular coffee table for sale now that uses two quite large slabs of sowbelley agate (below)