These old specimens of pyrite belong to one of those curiosities that Nature offers us. In these pieces we can see crystals those are showing no apparent cubic symmetry. They have, more or less marked, parallelepiped forms unusually flattened. The edges are completely natural and the crystal has been consolidated on its matrix to avoid its possible detachment.
This kind of crystals put into question certain aspects of the cubic symmetry of pyrite. For more information on this topic you can read articles like King & Prewitt 1979 (Amer. Min., 64, 1265-1271).