Origins of Blue Color in Sapphires from El Dorado Bar, Montana

SMSU Event Center BC

Heat treatment of sapphires can produce a richer more vibrant color in this gem, but not for all sapphire colors and localities. For this study, suite of sapphires was collected at the El Dorado Bar, Montana during the summer of 2018. The LAB color spectrum was measured for each of the sapphires, as well as sapphire weight and size. The sapphires were then sent for heat treatment at Gem Mountain Labs. The LAB color spectrum was then re-measured. The effectiveness of the heat treatment process was evaluated by a comparative analysis of the LAB color spectrum of untreated and heat-treated sapphires. The heat treatment enhanced the color of 38% of the pale blue to blue sapphires, while black sapphires showed no improvement or degradation of color. However, pink sapphires showed significant color improvement in hue, saturation, or both. Color of sapphires is dictated by traces of iron and titanium, coupled with heat from metamorphism. Since the heat treatment process can be expensive, knowledge of the treatment potential for specific localities and colors of sapphire will be useful in cost-benefit analyses in the gem industry. Future work will examine the chemistry of these sapphires to evaluate if the success of heat treatment was governed by limited iron, titanium, or metamorphic heat.