Here is an example of the use of X-ray Diffraction (XRD) to identify the crystal phases present in a TiO₂ sample.  Qualitative identification is based on the presence of the unique diffraction pattern for each phase, the "X-ray fingerprint". Positions and intensities of diffraction peaks are compared against the ICDD,  powder Diffraction File containing of reference patterns of more than 70,000 known phase crystalline materials. The sample was identified as a mixture of rutile and anatase as shown.

Figure 1.  Measured XRD pattern of TiO₂ mixture and its phases analysis.