The X-ray diffractometer beam path and detector

The wavelength I, chosen in advance, is constant and known, so that one only needs to know the angles d at which X-rays are diffracted to calcnlate the crystal lattice distances, d, from which the identity of the unknown mineral can be determined. 

In practice, for essentially all known minerals, the angles at which they diffract X-rays are known and tabulated in searchable databases. Modem diffractometers commonly use such databases to match the pattern obtained from an unknown sample to specific minerals, removing the need for calculating the crystal dimensions. 

In an actual apphcation, a small sample, 5-10 mg or more, would be taken from an artifact and crashed to a powder and mounted in the middle of the diffractometer. As the detector, as shown in Fig. 4.41, rotates around the sample, the computer counts the intensity of the X-rays at each angle and reports them in a graph as shown in Fig. 4.42. The angles at which the sample diffracts X-rays are then listed, along with their relative intensities, and compared to those in the searchable database. The computer then presents the closest matches to know minerals. In the example here, the material from an archaeological stone bowl is identified as the mineral chlinochlore. 

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