iron pyrite crystals in marl, La Roija, Navajun, Spain
Our top team pick! These cubes are completely natural and are still nestling in the marl they grew within. The white mineral on the surface is talc -- it forms as a by product of the crystal's growth.
At some point, we seem to be told that there is no such thing as straight lines in nature, and that cubes, right angles and geometric shapes are inherently artificial. In fact, all minerals have an underlying order: they consist of repeating atomic arrangements. These repeating atomic arrangements, determine the macrostructure of their crystals. Early mineralogists used the geometry and symmetries of crystals; particularly the relationship between their faces and edges, to deduce their unit cells (the smallest possible repeating unit that defines the symmetry of the resultant crystal). These unit cells were largely determined to be correct following the advent of x-ray crystallography in the early twentieth century.