Sapphire, like many other gem stones, is formed when minerals in the earth undergo transformations due to extreme heat and pressure. Chemically, sapphire refers to an aluminum oxide mineral called corundum that usually contains very small amounts of elemental impurities. The impurities are what give it a non-white color. If the impurities include iron and titanium, then the sapphire will be blue (which is the color most people think of when they hear ‘sapphire’). If the impurities include a lot of chromium, then the sapphire will be red – this is actually a ruby!