Tanzanite is a trade name of a gemstone, which is famous for its blue-violet color. It was discovered in 1967 in the Merelani Hills near Mount Kilimanjaro, Tanzania. Initially mistaken for sapphire, it was later identified as a blue-violet variety of the calcium aluminum hydroxyl sorosilicate mineral, zoisite stone (Ca2Al3(SiO4)3(OH))[1, 2].
In this application note, we prepared two small violet color stones as below and demonstrated the feasibility of micro-XRF for screening to distinguish a tanzanite gemstone and its imitation non-destructively.
Figure 1. A tanzanite gemstone and a tanzanite-like imitation glass stone.
The XGT-9000 X-ray Analytical Microscope (Figure 2) is an energy dispersive X-ray fluorescence microscope (micro-XRF) with an upper irradiation with micro-spot size and a motorized XYZ stage. The micro spot size is helpful to hit a limited surface on a small gemstone[3,4]. The motorized XYZ stage is helpful to analyze multiple samples set on a sample tray one by one.
Figure 2. (a) HORIBA XGT-9000 X-ray Analytical Microscope; (b) Schematic diagram of the internal optics of the XGT-9000; (c) Multiple sample setting on a sample tray.
We prepared two different small violet color stones. One is a real tanzanite gemstone from a reputable gemstone dealer, and the other one is a tanzanite-like imitation glass stone from a fashion accessory outlet. We placed the two small stones on a sample tray and set it into the XGT-9000 chamber.
We carried out point analysis on each stone using a 100 µm ultra-high intensity probe under full vacuum condition. Gemstones generally have crystalline structure, and the structure might cause diffracted X-rays, which could lead to undesired spectral interference with fluorescent X-ray peaks in a spectrum. For this reason, we used primary X-ray filters to reduce the undesired phenomenon during the analyses.
Figure 3a shows an optical image and an XRF spectrum of the tanzanite gemstone. The spectrum shows big peaks of oxygen (O), aluminum (Al), silicon (Si), and calcium (Ca), which are the main composition of a tanzanite stone (Ca2Al3(SiO4)3(OH)).
Figure 3b shows an optical image photo and an XRF spectrum of a tanzanite-like imitation glass stone. Although the optical image shows beautiful deep violet color like tanzanite, the XRF spectrum results show that there are no peaks of the main composition of tanzanite such as Al and Ca, and that there were clear peaks of non-exiting elements, such Zn and K.
Figure 3. Optical image and XRF spectra of (a) a tanzanite gemstone and (b) a tanzanite-like imitation glass stone. The analyses were conducted using the XGT-9000 Expert with a 100 μm ultra-high intensity probe under full vacuum condition. Primary X-ray filters and X-ray tube voltages were used to reduce the undesired diffracted X-rays during the analyses.
We confirmed that micro-XRF can be used to differentiate imitation color stones non-destructively, based on the elemental information.
[1] Gemological Institute of America, “Tanzanite Description”, [Online]. Available: https://www.gia.edu/tanzanite-description (accessed Oct. 20th 2025).
[2] Gemological Institute of America, “Gem Encyclopedia | Tanzanite | Overview”, [Online]. Available: https://www.gia.edu/tanzanite (accessed Oct. 20th 2025).
[3] HORIBA, “The Power of Micro-XRF in Gemology – Part 1: Small Garnet Characterization” HORIBA XGT Application Note, XGT-30. [Online]. Available: https://www.horiba.com/tha/scientific/applications/others/the-power-of-micro-xrf-in-gemology-part-1-small-garnet-characterization/ (accessed Oct. 20th, 2025)
[4] HORIBA, “The Power of Micro-XRF in Gemology – Part 3: Non-destructive elemental analysis on pearls on earrings” HORIBA XGT Application Note, XGT-37. [Online]. Available:: https://www.horiba.com/int/scientific/applications/others/the-power-of-micro-xrf-in-gemology-part-3-non-destructive-elemental-analysis-on-pearls-on-earrings-1/ (accessed Oct. 20th, 2025)
Application note XGT43 (2025)
