opal - The cause of the brilliant play of colors in opal was an enigma until relatively recently. Scanning electron microscope studies show that opals consist of transparent spheres of silica that are tightly packed. The voids or spaces between the spheres contain air or water. The regular arrangement of spheres acts as a diffraction grating, breaking visible white light into separate colors.
This is an extremely cheap laser diffraction grating which can be used, along with an ordinary laser pointer, to conduct the double-slit experiment and demonstrate the wave/particle duality of light. See http://en.wikipedia.org/wiki/Double-slit_experiment for further details on this experiment.
Though both financial audit and cost audit primarily aim at independent scrutiny of the accounts of an organisation yet they differ from each other in certain vital respects At http://www.theglobaltutors.com/Accounting-Homework-Help/Cost-Accounting/Financial-Audit-Cost-Audit