Allochromatic gems are gems that happen to be colored by impurities. If they had been completely pure, they'd be colorless. The color of all allochromatic gems is made by defects. So, all colour in corundum is a result of defects. Natural Pukhraj is actually a hugely coveted and precious gemstone, https://bookmarkswing.com/story19485872/examine-this-report-on-sri-lanka-yellow-sapphire