Our laboratory participated in the Proficiency Test titled "Determination of CaO, Al₂O₃, MgO, Fe₂O₃, and SiO₂ in Geological Samples (Natural Stone)" with the cycle code "MATYT-02-2026," organized within the scope of the TS EN ISO/IEC 17043 Standard by the Department of Mineral Analysis and Technology Laboratories under the General Directorate of Mineral Research and Exploration (MTA), using the WD-XRF instrument located in the GUTMAM Elemental Analysis Laboratories. According to the results obtained from the analyses performed, our laboratory achieved successful results for all elements. Through this study, the reliability of the analysis results and the measurement competence of the GUTMAM Elemental Analysis Laboratories have been demonstrated once again.