The Correlation of Colour and Iron Oxides in Yellow Seal Stones from Northern Laos

The yellow seal stone from northern Laos is one possible substitute for the Tianhuang Stone, most famous Chinese stone, because of its similar to orange-yellow appearance and same main mineral composition. colour causation was studied. samples’ phase, micro-morphology chemical components were studied by Raman spectroscopy, scanning electron microscopy (SEM) with energy disperse spectroscopy (EDS), respectively. mainly composed dickite, occasionally minor impurity minerals, such as hematite, anatase, barite, diaspore pyrite. Micro- nano-sized iron oxides/hydroxides observed detected SEM EDS in part samples. Moreover, these suggested cause Laos. UV-Vis spectrum second derivative, Kubelka-Munk spectra, used identify quantify hematite goethite. parameters obtained Commission Internationale de l’Eclairage (CIE) 1931 standard space. According observation samples results experiments calculations, parts (L* = 33.56~47.99, a* 0.35~3.65, b* 4.55~9.89) correlated goethite (goethite about 0.175~0.671 g/kg, content too low be figured out parts). In contrast, 33.99~46.27, 3.98~12.39, 8.04~22.14) more closely related 0.096~0.691 0.258~2.383 g/kg). correlation analysis also support that contents oxides or hydroxides influence colour. Therefore, it micro- nano-scaled caused stone. Hematite can strengthen red hue change orange-yellow.