Birthstones symbolize the month of your birth, and for those who believe the power of magical force which could protect the person who wear the stone. The birthstones were traditionally linked to the Zodiac; however the modern birthstones are lined to the calendar months.
The official modern birthstone list by the American National Association of Jewelers:
June Pearl or Moonstone
October Opal or Tourmaline
November Citrine or Yellow Topaz
December Blue Topaz, Turquoise or Tanzanite