Slab.
More than a mere square, much thicker than a foil, this is a slab. I acted as a transshipping point for a set of five of these on the way to Max Whitby at The Red Green and Blue company in England, sells a very nice element collection in several versions.
I chose this sample to represent its element in my Photographic Periodic Table Poster. The sample photograph includes text exactly as it appears in the poster, which you are encouraged to buy a copy of.