http://tilings.math.uni-bielefeld.de/tilings/substitution_rules/square_triangleQuasicrystals are aperiodic structures that produce Bragg diffraction, i.e. they show pure point spectra. Thus they share a defining property with crystals, but differ from them by lacking a regular repeating structure. They were considered to be mathematical artefacts, known as aperiodic tiling, but physical experiments gave evidence of their material existence. Within the field of crystallography and solid state physics the discovery has produced a paradigm shift which is indeed a minor scientific revolution. - from Wikipedia
