The birthstone for the Aquarius sign is amethyst. Garnet and jasper can also be considered birthstones under that sign as well.
Amethyst is believed to have energies from the planet of Uranus and is sympathetic to that planet. Those people who believe in astrology believe that wearing that gemstone will focus the energy of the planet and the sign through the gem, benefiting the person wearing the gem. The properties of the Amethyst birthstone include calm disposition, stability, sincerity, peace, courage, balance and inner strength. Amethyst stone is believed to have healing properties such as curing withdrawal symptoms associated with addiction.