Sapphire is the birthstone of September, the traditional gift on your 45th wedding anniversary and a material associated with both luxury and ruggedness. It can be found in opulent products like jewelry, camera lenses and fancy watches. Given that, it's also one of the toughest materials in the world, which makes it ideal for military-grade items like aviation displays and even missiles. So when rumors emerged that a sapphire display may be featured on the next iPhone, a chorus of excitement followed. However, many phone manufacturers don't share the same sense of optimism that Apple might hold toward this different kind of next-gen display.