Written with kind permission of Nicole E. Moore, Visiting Assistant Professor, Pomona College Geology Dept.

A crucial part of geological studies is the analysis of rocks, minerals and other solid samples. X-ray � uorescence (XRF) is regularly utilized for the elemental analysis of solid geological samples. Proper sample preparation is vital to ensure that XRF results are accurate and reproducible.

This article describes the important aspects of sample preparation for XRF, and how SPEX® SamplePrep can help you to prepare samples effi ciently and accurately in order to attain reliable XRF results.

Geological Analysis Examining the materials that our planet is made up of can teach us about its history, tell us about its present status, and help us make predictions regarding our future. An in-depth understanding of the composition of our Earth helps us to fi nd and protect our resources, including water, energy, and minerals.

In addition, it can help us to understand natural disasters such as volcanoes, landslides, and fl oods, and man-made disasters such as climate change. Geological studies are needed for every construction project to ensure that chosen sites are safe from contamination and other geological hazards, in addition to researching the major issues and problems of the world.1,2

Using XRF Analysis for Geological Samples

: : APPARATUS:ShatterBox®

Borate Fusion

: : Ring and puck mill

: : APP NOTE (SP028):Sample prepation of geological samples for XRF

SPEX SamplePrep65 Liberty StMetuchen, NJ 08840 USATel: 732-623-0465Fax: 732-906-2492E-mail: Sampleprep@spex.comwww.spexsampleprep.com

European HeadquartersSPEX Europe2 Dalston GardensStanmore, HA7 1BQ, UKTel: +44 (0)208 204 6656Fax: +44 (0)208 204 6654E-mail: spexeurope@spex.comWeb: www.spexeurope.com

Image credit: Pixabay/werner22brigitte

Grinding & Pulverizing

XRF Analysis is Crucial for Examining Geological SamplesWe must be able to characterize the structure, composition, and texture of geological materials in order to understand the materials of Earth. Analytical chemistry plays a key role in geological studies as a result. One of the most widely employed methods for measuring the elemental composition of geological samples is X-Ray fluorescence (XRF).3

XRF is an analytical method which calculates the elemental composition of solid samples. The sample is bombarded with X-rays, which excite the atoms present in the sample. As atoms relax, they emit fluorescence X-rays with characteristic wavelengths. Therefore, measuring the emitted fluorescence permits identification and quantification of the elements present in the sample.4

XRF is widely employed in a variety of applications as it is quick, easy to use, non-destructive, and cost-effective. It is especially suited to geological studies because it can analyze solid samples, while many alternative techniques of elemental analysis need sample dissolution, which can be problematic for many geological materials.3

Understanding Prehistoric Volcanic Eruptions with XRFA recent publication from Central Washington University and Oregon State University describes how researchers utilized XRF to characterize basalt rocks from the Steens Basalt, part of the Columbia River Plateau in Oregon USA.5

Approximately 17 million years ago, the area around the Columbia River experienced massive volcanic eruptions which covered an area of 53,000 km2 with lava, up to a kilometer thick in some places. As the lava flowed over the Earth’s surface, it cooled quickly and formed igneous rocks known as basalt.

The team of researchers utilized XRF to analyze trace and major elements present in the basalt rocks taken from several places in the Steens Basalt. Compositions of the samples supplied insight into the history of the rock formations, in addition to the volcanic eruptions which created them. (See figure 1 below.)

Sample Preparation is Key for Reliable XRFXRF is perfect for analyzing geological samples. Because XRF is known among geologists for being straightforward and quick, the importance of proper sample preparation is regularly overlooked. 6,7

Often, rock and mineral samples have varied particle sizes, rough surfaces, and non-homogenous compositions, which all decrease the accuracy of XRF results. To combat this, prior to XRF analysis, geological samples are ground into fine powders and formed into fused beads. Creating fused beads (in the form of discs) enables the most accurate XRF results for solid samples.6,7

By mixing the sample with a flux material (usually a lithium borate mixture) and melting the mixture using very high temperatures, the sample dissolves into the flux. Then, the molten mixture is formed into discs using a mold (see figure 2). The resulting discs give almost total sample homogeneity and take away the effects of particle size, surface roughness, and matrix effects, ensuring accurate XRF results.6,7

Figure 1. Stratigraphic height versus MgO, SiO2, Rb, and Ba in the Steens Basalt. Variations in chemical composition between the layers help distinguish them from each other. Image credit: Moore et al.5

The researchers understood how important preparing their samples properly for XRF was. By utilizing a SPEX ShatterBox®, the team ground their samples into fi ne powders (see fi gure 3) before forming fused discs and conducting elemental analysis. The result was reliable, consistent, XRF analysis with high reproducibility.5

SPEX SamplePrep are the Sample Preparation ExpertsPreparing samples for XRF can be time-consuming and tedious. The process of grinding hard geological samples into fi ne powders can be challenging. In addition, manual preparation of samples heightens the probability of error and cross-contamination.

Automated sample preparation optimizes workfl ow, saves time, and increases reproducibility. SPEX SamplePrep provides a variety of solutions to ensure your XRF sample preparation is hassle-free and reliable.8

The SPEX ShatterBox is a ring & puck mill in a soundproof enclosure which pulverizes brittle, tough samples within minutes. It is capable of grinding up to 150 grams to a fi ne powder and has become one of the most popular “swing mills” in America. The ShatterBox enables eff ective particle size reduction and homogenization, meaning it is perfect for preparing geological samples for XRF analysis and ensuring reproducible, accurate, results.9

Katanax® fusion fl uxers can be utilized to form fused glass beads after your sample is ground into a fi ne powder by the ShatterBox, ready for XRF analysis (see fi gure 4). Katanax fusion fl uxers are automatic electric fl uxers which combine speed, ease-of-use, and exceptional accuracy. They enable reliable sample preparation for accurate XRF results, every time.10

This information has been sourced, reviewed and adapted from materials provided by SPEX SamplePrep.

For more information on this source, please visit www.spexsampleprep.com

Shatterbox grinding containerFigure 3. Basalt sample ground in the Shatterbox

Figure 4. SPEX ShatterBox® (left) and Katanax® X-300 (right). Image credit: SPEX® SamplePrep.

Figure 2. Fused beads

References and Further Reading1. ‘Essentials of Geology (Fifth Edition)’ – S. Marshak, W. W. Norton &

Company, 2016.

2. ‘Engineering Geology and Construction’ – F.G. Bell, CRC Press, 2004.

3. ‘X-Ray Fluorescence Spectrometry (XRF) in Geoarchaeology’ – M.S. Shackley, Springer Science & Business Media, 2010.

4. ‘Handbook of Practical X-Ray Fluorescence Analysis’ – B. Beckhoff , B.Kanngießer, N.Langhoff , R. Wedell, H.Wolff , Springer, 2007.

5. ‘The three-stage petrochemical evolution of the Steens Basalt (southeast Oregon, USA) compared to large igneous provinces and layered mafi c intrusions’ – N.E. Moore, A.L. Grunder, W.A. Bohrson, Geosphere, 2018.

6. ‘Analysis of rocks using X-ray fl uorescence spectrometry’ – T.E La Tour, The Rigaku Journal, 1989.

7. ‘X-ray fl uorescence (XRF) in the investigation of the composition of earth materials: a review and an overview’ – T.D.T Oyedotun, Geology, Ecology, and Landscapes, 2018.

8. SPEX SamplePrep – www.spexsampleprep.com

9. SPEX ShatterBox – www.spexsampleprep.com/shatterbox

10. SPEX Katanax – www.spexsampleprep.com/katanax

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SPEX SamplePrep65 Liberty StMetuchen, NJ 08840 USATel: 732-623-0465Fax: 732-906-2492E-mail: Sampleprep@spex.comwww.spexsampleprep.com

European HeadquartersSPEX Europe2 Dalston GardensStanmore, HA7 1BQ, UKTel: +44 (0)208 204 6656Fax: +44 (0)208 204 6654E-mail: spexeurope@spex.comWeb: www.spexeurope.com