This study of yellow sapphires was motivated by The shortage of clarity within the literature as to the origin from the yellow coloration. Looking back, this uncertainty was the result of a few factors. To start with, the Fe3+ focus in natural stones spans A variety of about 4–4750 ppma, https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share