If you can get past the fact that they are "just" pyrites, you have to admit that these PERFECT cubes on matrix from Spain are amongst the most striking crystals in the mineral kingdom. Non-mineral people usually cannot believe that they form naturally, in fact! This specimen, looking like modern art, features a central cube 3 cm across, with three others cubes intergrown with it in a perfect arrangement on 3 different sides. A really amazing mineral specimen!