Identifying the trace element chemical fingerprint of blue colored quartz stones

Ellensburg Blues are a locally sourced blue quartz that retail for a higher price than blue quartz samples from other localities. We hypothesize that Ellensburg Blue samples have a distinct trace element fingerprint in comparison to blue quartz samples collected from other locations, such as Holley blue agates from Oregon. To test this hypothesis, multiple samples from known locations were analyzed using the Murdock Research Laboratories portable X-ray fluorescence spectrometer (pXRF). To gather a large enough dataset of known and unknown origin samples for analysis, this project analyzed samples from Carl Carlson’s Ellensburg Blue mine, the Kittitas Museum blue quartz collection, the CWU Geological Sciences collection, amongst others. Initial testing began with measuring the dimensions of each individual sample and then using the pXRF to perform bulk chemical analysis of the major and trace element compositions. The data was plotted based on its chemical composition, so similarities/differences between the samples could be identified. The Ellensburg blue samples have a distinct trace element composition with a spike in zirconium corresponding with the resulting blue color. The known locality samples were used to create ratios between various important trace elements to produce statistical relationships and develop the sourcing key for blue quartz samples. To test the key, we ran all of the samples from known locations and checked for a correlation i.e. an Ellensburg Blue was labelled as an Ellensburg Blue by the key. Our results showed that we can use the sourcing key to authenticate blue quartz samples as Ellensburg Blues