Birthstones by Astrological Sign
In 1912, a list of birthstones based on month was standardized in the United States by the National Association of Jewelers (now the Jewelers of America). They were chosen based on tradition, as well as which stones could realistically be sold by American jewelers. The official list has been updated, so you might see different birthstones for your month depending on where you look.
In addition to your birth month, you can find a birthstone for your Western astrological sign. Note: There isn’t an official standardized list of birthstones based on astrological signs, but there are some traditional associations.