Sapphire is a variety of corundum, an aluminium oxide, and occurs in many different colours (such as blue, yellow, pink, green, orange). Any corundum gem that is not red is called sapphire. You should assume that all sapphires on the market have been heat treated unless stated otherwise. Padparadscha is a very rare and valuable variety of sapphire, with a pink/orange colouring. Be wary of inexpensive beads marketed as 'Tunduru sapphire' - they are often multi-coloured garnet. Birthstone for September. Hardness: 9 (Mohs).