Beautiful pyrite mineral specimen on the host rock from Spain. This locality's limestone matrix can dissolve in water, so the specimens matrix needs to stay dry for these pyrite cubes to stay in place.
FYI: When mined, these pyrite cubes typically do not stay in place on the host rock unless buried deep within the matrix. Almost all of the on matrix pyrite specimens have been stabilized with some sort of epoxy or glue to keep the cubes in place. The pyrite crystals and the host rock are all natural, and it is very common that many of these Spanish pyrite specimens have been reassembled, just as they were within the earth.