Allochromatic gems are gems which are coloured by impurities. If they were being entirely pure, they would be colorless. The color of all allochromatic gems is made by defects. So, all shade in corundum is because of defects. What is most unconventional is always that this first cost transfer band https://socialfactories.com/story3440669/natural-pukhraj-from-sri-lanka-things-to-know-before-you-buy