Have you ever seen a coin dropped on the street on a warm day? It will become embedded in the hot asphalt and wear away over time. depending on the composition of the coin, the plating or the face may wear away, leaving only a metal disk.
This long-term process is recreated in these pieces. Coins are inserted nearly flush with the floor. They aren't meant to be noticed easily, but walked on and slowly abraded, their texture eventually wearing away, becoming part of the surface in which they are embedded.