Base after grouting the tile.

The marble tile pieces started as two 12" square tiles from the big-box store. I pulled the pieces off the netting, spent about two hours arranging them, and broke a few and sanded the edges straight to close out a few gaps in the edges (esp. lower right corner).

The little squares are pieces of 3/8" thick MDF that I punched 1/4" square holes into using the chisel from a mortise bit. I measured, and measured, and measured again before and after gluing them in place, which paid off as they were each as close to the intended location as I could measure with the tools available. (Whew!)

The grout was the premixed "silver" color paired with the tile in the store display. When I mixed it I could see it would clearly be too bright, so I added a few drops of Old Mission and Brown Mahogany wood dyes to the mix. The results when dried were just a little lighter than shown here. I then sprayed it with a few coats of a matte acrylic sealer, which was a little shinier than I wanted but close enough.

It was only when I had everything glued that I A) realized I had a sizeable gap just right of center, and B) remembered that I had a box of small Petoskey stones (fossilized coral from northern lower Michigan) that I had intended to use for this project. Derp. At least I managed to squeeze in one of them.