“In this regard, the following statements can be meet for the opal: the anisotropy, so direction depending on a physical property, is given at the opal alone through the color game.” A body is also the opal that he is shape and volume stability. In addition the opal is uniformly constructed with a three-dimensional periodic arrangement of its elements, here the silica beads in the form of Dichtestpackung. Therefore, all conditions are met, also to see the opal as Crystal. Only not just on an atomic level, but on a different scale – the wavelength of visible light. Is used as a distinguishing criterion amorphous/crystalline interaction with x-rays, an opal is amorphous though, but the opal-typical play of colours is also described with the Bragg law known from X-ray diffraction to light the opal behaves crystalline 3. Actually scientists of the Gemmological Institute could show in Nantes (France), that behaves an Opal as a light Crystal and (similar to atomically structured crystals in the interaction with X-rays) illumination with white light a characteristic diffraction pattern observed is: “Perfect diffraction in an opal from Wollo, Ethiopia” is a further characteristic of the Crystal the optical anisotropy, which was occasionally observed at Edelopalen, whose cause is settled but only in 2010.
In the article “Rontgenamorph and crystalline light – optical properties of Grandpa liner materials” 3 is proved that opals show not only an optical anisotropy, but that this property is similar to the behavior of Atomic and optically uniaxial crystals. For the first time, a Maltese cross, the typical interference pattern of optically uniaxial crystals, was observed at Edelopalen and documented. Additional information can be found on the page “Optical properties of the opal”. The opal is therefore a x-ray amorphous, but also light crystalline gem and against the use of the term “Crystal Opal” is to be nothing in the future.