Pyrite usually forms cuboid crystals, sometimes forming in close association to form raspberry-shaped masses called framboids. However, under certain circumstances, it can form anastomosing filaments or T-shaped crystals. Pyrite can also form shapes almost the same as a regular dodecahedral, known as pyritohedra, and this suggests an explanation for the artificial geometrical models found in Europe as early as the 5th century BC. Pyrite is distinguishable from native gold by its hardness, brittleness and crystal form. Natural gold tends to be irregularly shaped, whereas pyrite comes as either cubes or multifaceted crystals. Pyrite can often be distinguished by the striations which, in many cases, can be seen on its surface.