Analysis of Gemstones Using EDXRF

Energy Dispersive X-Ray Fluorescence (EDXRF) is a crucial tool in ascertaining the legitimacy and geographical origin of colored gemstones.

Precious gemstones like rubies, emeralds, or sapphires from diverse sources display characteristic combinations of trace elements at varying concentrations, contingent on the geological context.  

By identifying and quantifying these elements, it becomes possible to trace the origin of an emerald, pinpointing its location, be it Colombia, Brazil, Afghanistan, Zambia, or Zimbabwe.  

The presence of specific trace elements aids in distinguishing between valuable naturally formed gemstones (e.g. ruby) and relatively worthless synthetic crystals (e.g. synthetic ruby).

Analysis of Gemstones Using EDXRF

Image Credit: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

Instrumentation

The Thermo Scientific ARL QUANT’X EDXRF Spectrometer proves highly suitable for non-destructive gemstone analysis. The instrument’s Silicon Drift Detector (SDD) boasts a generous area of 30 mm², ensuring excellent detection efficiencies for crucial elements like gallium (Ga) in rubies.  

The instrument's direct excitation geometry and adjustable X-Ray beam collimation allow analysis with small yet precise spots while retaining exceptional analytical sensitivity. Various X-Ray beam collimators are available to fine-tune the spot size.  Including a sample imaging CCD camera further facilitates the positioning of small gemstones, optimizing the efficiency of excitation and analysis processes.

Table 1. Analytical settings. Source: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

Voltage (kV) Tube filter Atmosphere Live time (s) Elements
4 No Filter Vacuum 120 Na, Mg, Al, Si
8 C Vacuum 60 Ca
12 Al Vacuum 60 Ti, V, Cr, Mn
16 Pd Thin Vacuum 60 Fe, Ni
20 Pd Medium Vacuum 30 Cu, Zn, Ga, W, Ir, Pt, Au
28 Pd Thick Vacuum 30 Pb, Zr, Mo
40 Cu Thin Vacuum 30 Ag, Pd, Sn

 

Excitation Conditions

The ARL QUANT’X Spectrometer features a 50 Watt X-Ray tube, providing a wide range of excitation voltages (4-50 kV) that can be adjusted in increments of 1 kV.

The spectrometer has nine primary beam filters to optimize background control and enhance elemental sensitivity, improving peak-to-background ratios and overall performance.  

Table 1 outlines the excitation conditions utilized for analyzing rubies and emeralds. The tube current is automatically optimized to reduce the detector's dead time, and each analysis takes less than 10 minutes, all performed under vacuum conditions.

Sample Preparation and Presentation

To preserve the integrity of the gemstone samples, they undergo analysis without any damage. Small gemstones are mounted on a custom-made sample holder or placed in an XRF cup, sealed with a 4 μm thick polypropylene film.

Calibration

For calibrations, a Fundamental Parameter (FP) approach is employed and included in the standard quantitative package of the ARL QUANT’X Spectrometer. The calibration process involves using a set of 20 easily accessible pure element and compound standards.  

These standards are preferred over pure minerals or crystalline gemstones, as they are amorphous and do not exhibit any diffraction peaks in the spectrum.  

Thermo Scientific offers dedicated standards and calibration methods specifically designed for gemstone analysis.

Analysis Results

Multiple synthetic and natural rubies, sapphires, and emeralds underwent examination using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), a reliable and semi-non-destructive analysis technique commonly utilized as a reference for gemstone analysis.  

The results were then compared to those obtained from the ARL QUANT’X Spectrometer. Table 2 compares concentrations found for various rubies and sapphires, while Table 3 showcases the analysis results for emeralds. All analyses were conducted using a 2 mm X-Ray beam collimator.

The data indicates a strong agreement between the EDXRF and LA-ICP-MS results, with most concentration differences falling within the uncertainty interval determined by the standard deviation.

Table 2. Analysis results for rubies and sapphires (conc. expressed as % w/w). Source: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

Synthetic ruby Douros, 4.80 ct
  Al2O3 TiO2 V2O3 Cr2O3 Fe2O3 Ga2O3
Conc. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev.
LA-ICP-MS 99.5 0.0015 0.001 0.0000 0.0001 0.883 0.428 0.048 0.006 0.043 0.003
ARL QUANT’X Diff. 0.0029 0.0016 0.000 - 0.792 0.004 0.024 0.001 0.032 0.001
Synthetic pink sapphire, 1.405 ct
  Al2O3 TiO2 V2O3 Cr2O3 Fe2O3 Ga2O3
Conc. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev.
LA-ICP-MS 99.5 0.0027 0.0002 0.0000 0.0001 0.0299 0.0002 <DL - 0.0000 0.0001
ARL QUANT’X Diff. 0.0029 0.0008 0.000 - 0.0334 0.001 0.000 - 0.002 0.001
Natural Shadong sapphire, 1.784 ct
  Al2O3 TiO2 V2O3 Cr2O3 Fe2O3 Ga2O3
Conc. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev.
LA-ICP-MS 99.5 0.0208 0.0014 0.0030 0.0003 0.0045 0.0032 1.182 0.043 0.029 0.002
ARL QUANT’X Diff. 0.0195 0.0015 0.0028 0.0008 0.0034 0.0006 1.043 0.006 0.027 0.001
Synthetic brown star sapphire, 3.935 ct
  Al2O3 TiO2 V2O3 Cr2O3 Fe2O3 Ga2O3
Conc. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev.
LA-ICP-MS 99.5 0.096 0.006 0.398 0.015 0.0112 0.0004 <DL - 0.0000 0.0001
ARL QUANT’X Diff. 0.110 0.003 0.349 0.004 0.0130 0.0012 0.000 - 0.000 -

 

Table 3. Analysis results for emeralds (conc. expressed as % w/w). Source: Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers

Natural emerald, Pakistan, 1.022 ct
  NaO MgO AlO SiO
  Conc. Std Dev. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev.
LA-ICP-MS 1.95 0.04 2.37 0.03 14.25 0.36 65.22 0.40
ARL QUANT’X 2.04 0.16 2.33 0.06 12.86 0.10 65.74 0.10
  ScO VO CrO FeO
  Conc. Std Dev. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev.
LA-ICP-MS 0.461 0.032 0.074 0.005 1.40 0.27 0.256 0.007
ARL QUANT’X 0.500 0.005 0.080 0.002 2.00 0.01 0.318 0.004
Synthetic emerald, Gilson flux grown, 1.43 ct
  NaO MgO AlO SiO
  Conc. Std Dev. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev.
LA-ICP-MS 0.104 0.002 0.0033 0.0001 19.35 0.22 67.12 0.40
ARL QUANT’X - - 19.29 10.08 67.22 0.11
  ScO VO CrO FeO
  Conc. Std Dev. Conc. Std Dev. Conc. Std Dev. Conc. Std Dev.
LA-ICP-MS 0.00023 0.00001 0.072 0.004 0.363 0.007 0.046 0.001
ARL QUANT’X - 0.092 0.002 0.436 0.001 0.062 0.002

LA-ICP-MS data generated by and property of Dr. M.S. Krzemnicki, Swiss Gemmological Institute SSEF.

Conclusion

This article demonstrates the application of the ARL QUANT’X EDXRF Spectrometer in gemstone analysis. Employing a simple calibration method with pure elements or compounds yielded results closely aligned with LA-ICP-MS data.  

Consequently, the ARL QUANT’X Spectrometer is a cost-effective and genuinely non-destructive analytical tool for gemological laboratories. Beyond rubies, sapphires, and emeralds, this approach can be applied to the analysis of other precious stones like spinels, chrysoberyls, and even pearls.

Acknowledgments

Thermo Fisher Scientific would like to thank Dr. F. Herzog and Dr. M.S. Krzemnicki of the Swiss Gemmological Institute SSEF, Basel, Switzerland for sharing the LA-ICP-MS data as well as offering their valuable expertise regarding gemstone authenticity, origin and chemical fingerprinting.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers.

For more information on this source, please visit Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers.

Citations

Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Thermo Fisher Scientific - Elemental and Phase Analysis. (2023, August 30). Analysis of Gemstones Using EDXRF. AZoM. Retrieved on December 10, 2023 from https://www.azom.com/article.aspx?ArticleID=10880.

  • MLA

    Thermo Fisher Scientific - Elemental and Phase Analysis. "Analysis of Gemstones Using EDXRF". AZoM. 10 December 2023. <https://www.azom.com/article.aspx?ArticleID=10880>.

  • Chicago

    Thermo Fisher Scientific - Elemental and Phase Analysis. "Analysis of Gemstones Using EDXRF". AZoM. https://www.azom.com/article.aspx?ArticleID=10880. (accessed December 10, 2023).

  • Harvard

    Thermo Fisher Scientific - Elemental and Phase Analysis. 2023. Analysis of Gemstones Using EDXRF. AZoM, viewed 10 December 2023, https://www.azom.com/article.aspx?ArticleID=10880.

Comments

  1. Fasiulla Khan Fasiulla Khan India says:

    What is the cost of the machine

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoM.com.

Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Your comment type
Submit