Allochromatic gems are gems which might be coloured by impurities. If they ended up fully pure, they might be colorless. The color of all allochromatic gems is made by defects. Therefore, all colour in corundum is caused by defects. Delhi is the principle destination for gem fans, and it is https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share