X-ray diffraction

X-ray diffraction (XRD) is a rapid analytical technique used for the quantitative determination of the minerals present in crystalline material such as rocks, soils and synthetics. The method depends upon the unique structural properties of crystals of those minerals, whose response to the x-ray beam is determined by the organisation and dimensions of their regular atomic structure.

Our sister company X-ray Mineral Services, are experts at quantification of whole rock and clay fraction samples using industry standard methods, modern XRD machines and over 50 years combined experience in analysing the data produced. XRD quality control is maintained using internal calibration against known mineral standards and external checks using regular international round robin proficiency testing which includes the Reynolds Cup competition.

Bulk sample quantitative phase analysis is performed, when possible, with the Rietveld method using one of the software packages we have available (e.g. AutoQuan, Siroquant and HighScore Plus). When this is not possible, for example due to a lack of published mineral structure models, we will perform quantification using our in-house normalized Reference Intensity Ratio method (RIR). This is a RIR method that has been calibrated for the instruments by measuring more than 250 reference minerals and mixtures. Qualitative analysis is backed-up by use of internationally-recognised reference libraries of XRD patterns which continue to be improved and augmented.

X-ray Mineral Services are experts in the analysis of clay minerals. Although they might be evident in the bulk sample diffractograms, the most satisfactory method for their identification and quantification is to extract and analyse the <2 micron clay fraction separately. The clay fraction is subjected to 4 different thermo-chemical treatments that allow the unambiguous phase identification of small quantities of clay minerals, including mixed-layer clays.

While the XRD powder method is in widespread application as the best for quantitative analysis of natural mineral samples, there is significant variation in the preparation techniques of laboratories, the variety of instrumentation they operate or the employment of different interpretation software. These variations can affect the outcome and the only way to confirm the accuracy and precision of the method when applied to natural samples is to check against synthetic mixtures of appropriate mineral standards.

X-ray Mineral Services participates in Quantitative Phase Analysis (QPA) international round-robin proficiency tests, including the Reynolds Cup competition and we routinely prepare our own standard mixtures to validate our sample preparation and QPA methods.

In addition to XRD, we also offer mineral identification and semi quantification by infra-red spectroscopy. Our FTIR instrumentation can be tailored to analyse many different sample types in a time and cost effective manner. FTIR also has the advantage of being portable and can be taken to the client’s site.