There are birthstones for the month in which you were born, but an alternative system assigns birthstones to your sign of the zodiac. Astrological birthstones predate monthly birthstones, coming from a time when it was considered wise to consult your astrologer rather than your jeweler before purchasing a gem. Note that some signs have ambiguous beginning/ending dates. People born on these dates are said to be 'on the cusps' or to have 'borderline dates'. If you are born on a cusp date, your sign depends on the time, date, and place of your birth.
Birthstones for Signs of the Zodiac 
