Sapphire is the birthstone for September, and one of the "Big Three" colored gemstones along with emerald and ruby. It is one of the most popular colored gemstones in the world, and especially the United States.
Sapphire symbolizes nobility, truth, faithfulness, and sincerity. As such, it is the most popular colored stone to be used in engagement rings. Sapphires actually predate diamonds in engagement rings.
Along with its sister stone ruby, sapphire is a variety of the mineral corundum. A corundum colored anything but red is a sapphire, and there are many colors. Sapphire comes in the well-know blue, pink, yellow, orange, purple, green, and colorless. A rare and valuable color is the pinkish-orange padparadscha sapphire. This comes from a derivative of the Sanskrit word meaning lotus color. Red corundum is a ruby. Corundum rates a 9 on the Moh's hardness scale, which makes it the hardest gemstone other than diamond. Because of this, sapphires and rubies are the best colored stones to wear in rings, where hardness is a factor because of all the bumps that a ring will take in its lifetime.
Some sapphires can present one of a few types of phenomena. Some have so much of a silk-like inclusion that they will show asterism, or a star, if cut correctly. Others will change color depending on the type of light they are seen in, similar to alexandrite.