The concept of birthstones trace back to the writings of Josephus and St. Jerome, who made references to a ceremonial garment known as the Breastplate of Aaron. According to them, the twelve stones on the breastplate were tied to the twelve months of the year, along with the twelve zodiac signs. From there, it was a small step to assigning a jewel to the date of one’s birth.
Due to quirks in classification, many regions and eras had their own ideas of what jewel represented which month. The first standardized list came out in 1912, penned by the American National Association of Jewelers, with later lists penned by different organizations.
Today, while different birthstones are associated with different traits, such as loyalty, most wearers attach other meanings to these jewels. Some may feel partial towards a stone for its association with the birthdate of a loved one or other special events associated with their personal lives.