How are sapphires formed?

Sapphires form deep in the Earth’s crust when corundum, the mineral, crystallises under severe heat and pressure. During that process, tiny amounts of iron and titanium seem to interact in a way that builds the stone’s usual blue tone.

Even if blue gets the most attention, sapphires can appear in many other colours, except red. When the red comes, it gets put in a ruby category instead. The exact hue depends on which trace elements are present while the crystal is growing. In nature, they are usually collected from alluvial deposits or from primary igneous rock bodies, especially in well-known gem regions like Sri Lanka, Madagascar and Australia.