Because gemstones form under unique circumstances, each individual gemstone is comprised of a combination of trace minerals, which create a unique set of identifying marks or inclusions.

Because sapphires are more commonly found in nature, those chosen to be set in jewelry often have higher clarity levels than rubies, but internally flawless sapphires are very rare. Because rubies are very rare, internally flawless rubies are extremely rare. Exceptional gemstones with few or no inclusions are available, but they command extravagant prices. For the best value, look for sapphires that are moderately included, and rubies that are heavily- to moderately-included.