A concept of “first measure, then determine” which elements are of interest is introduced for multi-element analysis using LA-ICP-TOF-MS. Geochemical data visualization using t-SNE is advantageous over PCA for determining the provenances of emerald.

Gem-A - the world's longest established provider of gem education.

Gem-A - the world's longest established provider of gem education.

Gem-quality rubies and sapphires are often commercially heat treated at about 800 °C or higher to enhance their color and clarity, and hence quality. For this study, selected corundum samples containing diaspore and goethite inclusions were heated step-by-step to a maximum of 1000 °C with the aim of monitoring the dehydration and phase transformation of these oxyhydroxides to corundum and hematite during heating. Based on our experiments and in agreement with the literature, the dehydration of diaspore in corundum occurs between 525 and 550 °C, whereas goethite transforms to hematite between 300 and 325 °C. As both diaspore and goethite may be present as inclusions in rubies, sapphires, and other corundum varieties (e.g., pink sapphires, padparadscha), these dehydration reactions and phase transformations can be considered important criteria to separate unheated from heated stones, specifically in cases in which other methods (e.g., microscopy, FTIR) are unsuccessful.

Gem-A - the world's longest established provider of gem education.