What Your Birthstone Meant in the Middle Ages

Most of us today are probably familiar with the concept of birthstones—precious gems associated with each month, like a petrological Zodiac. It turns out birthstones are more or less an invention of modern jewelry manufacturers, whose meanings all boil down to “Buy this ring.” But this is boring. So I thought, why not make birthstones mean something today by looking at their superpowers according to the Middle Ages?