The Ruby is July's birthdays' gemstone and the stone for 15th and 40th anniversaries. It is distinguished by its vibrant red color. It is both scarce and durable, second only to the diamond. Its durability makes it an excellent stone for use in jewelry. The fact that it is scare makes it very expensive . . . large stones can be more than two or three times the price of a diamond, comparable in size and quality. The Ancients thought that rubies "caught" a spark from Mars, the red planet. They believed that it could cure diseases and "motivate" couples to reconcile quarrels.