Allochromatic gems are gems which are coloured by impurities. Should they had been completely pure, they'd be colorless. The colour of all allochromatic gems is made by defects. Thus, all coloration in corundum is caused by defects. Beware glass-stuffed Ceylon Yellow Sapphires. They might glance shiny However they circumvent the https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share