Your Birthstone Guide: Discover the Gem for Every Month Before plunging deep into Birthstones By Months, firstly, it's important to understand what is birthstones. A birthstone is a kind of gem or a crystal that helps to represent a person’s birth period, especially the month or zodiac sign. The history of birthstones found its roots back to ancient civilizations and is steeped in tradition, belief and custom. The idea of birthstones may have originated from the breastplate of Aaron, which contained 12 gemstones representing the 12 tribes of Israel.