Allochromatic gems are gems that are coloured by impurities. Should they have been totally pure, they would be colorless. The color of all allochromatic gems is produced by defects. Thus, all coloration in corundum is brought on by defects. Burma is renowned for manufacturing a variety of valuable gemstones, from https://hotbookmarkings.com/story18107003/sri-lankan-yellow-sapphire-an-overview