How can you identify a natural sapphire?

Natural sapphires can be checked by spotting angular colour zoning, hexagonal growth lines, or real mineral inclusions such as intersecting rutile silk when viewed under 10x magnification.

Since sapphires share the same corundum crystal structure as rubies, the identification methods overlap quite a bit. When you see straight, sharply angled colour bands, that is a strong hint that the stone is natural and unheated. For lab-made sapphires, you often find curved colour banding or even interiors that are perfectly clean. That level of clarity is uncommon in nature, so it can stand out.