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In a study of an archaeological artefact thought to be a mask of Coptic Egyptian origin, a fragment was inspected using powder X-ray micro-diffraction to explore the possibility of identifying pigments and/or fillers in the paintwork applied to the surface of the mask. X-Ray diffraction data were collected with a Bruker D8 Discover diffractometer with Cu-Ka radiation (l = 1.5406 ) operating in parallel beam geometry collimated to 2 mm. Data were collected were collected from three separate sample sites with coupled q-2q scans in the 2q-range 5-80 with dwell time of 0.5 s for each 0.02 increment. The fragment studied is shown in the Figure below. Its surface is uneven and the fabric coating appears to be composed of a blue-green upper layer above a white, grainy sub-layer. Preliminary XRF studies have identified the presence of copper, calcium and silicon

(a) Briefly explain the terms microdiffraction and why parallel beam geometry might be an advantageous choice in the analysis of the uneven surface of the sample. Illustrate your answer with a suitable diagram