Allochromatic gems are gems that happen to be colored by impurities. If they had been completely pure, they would be colorless. The colour of all allochromatic gems is produced by defects. Hence, all shade in corundum is brought on by defects. Beautiful bit of jewelry- very well built. Not too https://mnobookmarks.com/story18025124/sri-lankan-yellow-sapphire-for-dummies