XRD (X-Ray Diffraction) is another analytical technique available to scientists. In this instance, however, it is not light that is interacting with the sample, but rather x-rays. XRD can only be used to analyze solid substances, and neither liquid nor gaseous samples, as the technique is based on the interaction between x-rays and the established crystalline structure of the material. In order to test a sample, it must first be finely ground up. The powder is then placed in the machine which, in essence, fires x-ray beams at the sample from all possible angles (2θ) and records the constructive interference created between the structure of the sample and the x-ray beams Louër 2006