Birthstones are precious or semi-precious gemstones associated with each month. Gem researchers believe that assigning meaning to birthstones began with the Bible's Exodus 28:15-30. This passage describes the Breastplate of Aaron, a ceremonial garment adorned with twelve gemstones representing the twelve tribes of Israel.
Depending on the culture and throughout history, a variety of gemstones have been identified as birthstones. There is no universal agreement as to a single, particular birthstone for each month.
In the United States, however, the National Association of Jewelers designated a modern birthstone list in 1912. Even this list, however, fails to list a single birthstone for each month. Rather, the list also includes alternatives (for example, in 2002, tanzanite was added as a December birthstone).
The list below is the list of generally accepted birthstones (one for each month) in the United States.