The practice of associating certain gemstones with certain months of the year dates back at least 2000 years. George Frederick Kunz, a mineralogist and gemologist who served as the Vice President of Tiffany & Company in the late 1800s, wrote in his book, The Curious Lore of Precious Stones:

“The origin of the belief that to each month of the year a special stone was dedicated, and that the stone of the month was endowed with a peculiar virtue for those born in that month and was their natal stone, may be traced back to the writings of Josephus, in the first century of our era, and to those of St. Jerome, in the early part of the fifth century. Both these authors distinctly proclaim the connection between the twelve stones of the high-priest’s breastplate and the twelve months of the year, as well as the twelve zodiacal signs.” [1]

“However, in spite of this early testimony, we have no instance of the usage of wearing such stones as natal stones until a comparatively late date; indeed, it appears that this custom originated in Poland some time during the eighteenth century.”