It seems to be a cultural thing for the ladies of Earth to be wearing pearls and/or diamonds for jewels, especially among nobles, royals, and people who could afford them.

A lot of women back at home tend to wear pearls a lot, it seems to be a suitable gem for both day and night time events. Diamonds meanwhile tend to be prized for many around the world. I had always assumed that my parents thought that by letting us slowly build up on these gems instead of maybe buying them in bulk or just buying ready to made jewelry so often, we could have them be made into necklaces in any style we wanted or we could go the traditional single strand style.