This review of yellow sapphires was motivated by The dearth of clarity inside the literature as to your origin in the yellow coloration. On reflection, this uncertainty was the results of a few variables. Very first, the Fe3+ focus in natural stones spans a range of somewhere around 4–4750 ppma, https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share