Allochromatic gems are gems that are coloured by impurities. Should they had been fully pure, they would be colorless. The colour of all allochromatic gems is produced by defects. Hence, all coloration in corundum is due to defects. Pukhraj stones are believed for being potent talismans that convey very good https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share