Birthstones have an ancient history, but the list of modern birthstones was only standardized in 1912 by the National Association of Jewelers, with a few updates since. The most commonly accepted list of the 12 modern birthstones is garnet (January), amethyst (February), aquamarine (March), diamond (April), emerald (May), pearl (June), ruby (July), peridot (August), sapphire (September), opal (October), citrine (November) and topaz (December).