The minerals, chemical, and other physical characters remaining the same. The process produces flawless, larger gems at very affordable prices. The gem will never change colour or go bad, rather will look stunning forever. Blue Sapphire is the September Birthstone. Blue Sapphire is the most popular of all gems. It is a very hard gemstone coveted for its vivid blue colour. Colour zoning is responsible for certain Sapphires having lighter and darker colours in different parts of a crystal. Some Sapphire gemstones may even be multicolored such as purple and blue. Sapphire is a tough and durable gem, and the only natural gemstone harder than Sapphire is Diamond.