Blue Sapphire 4.0 Carat Emerald-Cut 925 Sterling Silver Ring Size 6 Sapphire is a precious gemstone formed from a mineral called corundum. Blue Sapphires get their color from titanium and iron trace elements. Blue Sapphire rates 9 out of 10 on the Mohs scale of mineral hardness, making it a very durable gem. The word 'sapphire' comes from the Greek word sapphirus, which means blue. Sapphire, particularly the deep blue variety, has been associated with and beloved by royalty for centuries. Medieval kings wore sapphires; many believed the gems would protect them in battle.