system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did the various birthstones get associated with each month?
gpt
In 1870, the jewelry company Tiffany and Co. created an advertising campaign around the birthstones. Previously, there have been some theological/astrological debates about assigning a gem to each of the 12 signs of the zodiac or the 12 apostles, and the company kinda messed around with the traditional listing to make sure they only included Tiffany's stock of gems. The list then took a life of its own and the various jeweler's association around the world took it up as a convenient marketing symbol. They "updated" the list something like 3 times and the US and England both have different lists.

Basically, a Jewelery company ran an ad campaign to encourage the sale of the "lesser" gems like garnet and topaz.