This is really cool and I didn’t know it existed. Penn State University has an obelisk containing a variety of local rock types that has stood since the 1880s. The rocks were approximately placed in geologic order (although more recent work has updated some of the numbers).
Since it has stood for 130 years, it has turned into a great experiment in weathering. As the rocks are exposed to the atmosphere, more easily weathered rock types have retreated, while more resistant rocks have held their ground.