Mineral and rock analysis by XRD 

The XRD laboratory at SGU undertakes analytical identification and characterisation of minerals, both as separate phases and mixtures (rock samples), as well as determination of their respective proportions in rocks.  We also analyse clay mineral-bearing samples, with emphasis on the detection of swelling clays.

The X-ray diffraction (XRD) laboratory at the Geological Survey of Sweden (SGU) is situated at the head office in Uppsala. Be­sides in-house use, our mineralogical laboratories, that also include capacity for polarized light microscopy and Raman spectro­scopy, are open for external contract work.

Identification of crystalline compounds

We undertake analytical work including characterization of minerals, both in the form of individual monophase samples or in mixtures such as rocks, ores and industrial minerals and building materials. The XRD method supplies the user with direct information on the mineral phase or phases present, unlike the various methods of whole rock chemical analysis often used.

Quantitative analysis

After initial analysis and identification of the individual minerals present in a sample, additional analysis and treatment of raw data files by a computer-aided Rietveld refine­ment technique allows for semi-quantitative determination of the proportions of most major crystalline phases present. This combination of methods results in both identification and quantification of the minerals in the sample, thus giving a uniquely complete package of material information. It also allows for comparatively rapid analysis, in contrast to traditional methods such as thin section petrography, where not least time spent waiting for sections being prepared may be significant. Under special circumstances, a complete characterisation of the sample may be had the same day as it is submitted to the XRD laboratory.

A multitude of uses

The combination of identification and quantification by XRD can be used to an advantage in many fields beside the normal modal classification of rocks. Other uses include the characterization of key minerals and their contents in building material and road material, determination of contents of quartz and/or other hazardous species in crushing or building operations, assessment of rock properties for technical/mechanical designs, assessment of heat conductivity for geothermal energy investigations, as well as all fields of mineral prospecting, including the detection and characterisation of alteration halos related to ore mineralisation and studies of industrial minerals.

Clay mineral analysis

The preparation and analysis of clay minerals is focused on the detection of swelling (expanding) clay phases such as smectites, which are problematic and hazardous in various types of building endeavours, particularly in tunnel projects and general underground bedrock construction work. More in-depth analyses of fine/clay fraction mineralogy can also be performed on request.

Equipment

The mineralogical laboratory facilities at the Geological Survey include a well-equipped preparation laboratory, among other featuring extreme fine-grinding (micronising) capacity and a line for production and treatment of oriented clay mineral samples.

The core of the lab is a modern Siemens/Bruker D5000 diffractometer. It is a theta-theta type instrument with Bragg-brentano geometry, meaning that it can also accomodate unstable samples including fluids. It is equipped with rotating sample holder and variable slits, which are advantageous for certain quantitative analyses.

Diffractograms are recorded and accessed via a computerised system, which together with Bruker Advanced X-ray Solutions software packages of the DiffracPLUS family allows extensive assessment and evaluation. Another analytical capacity of the lab is software allowing for quantification of (crystalline) phases in mixtures.

Raman spectroscopy

Besides traditional polarized light microscopy (reflected and transmitted light) capacity, the mineralogical laboratory also includes a basic laser-Raman spectrometer.

The Raman method is useful for characterisation and analysis of various materials, including minerals. The method is normally non-destructive, and utilises a 785nm laser beam to irradiate the sample. This results in different types of spectra that are characteristic for discrete molecules in the studied sample.
Analyses can be performed on a multitude of sample types, among others loose crystals or crystal/mineral fragments, mineral inclusions or phases present in hand specimens, normally without any prior sample preparation. This makes the Raman technique highly suitable for identification and characterisation of sensitive or valuable samples or objects, such as gemstones in jewellery or archaeological samples or artefacts. The instrument is mobile and can be utilised in the field or at most other locations, as required.

More information: Erik Jonsson