Birthstones often have swashbuckling histories, but for me, one of the swashbuckling-est is emerald.
I always think of Spanish conquistadores, those blood-thirsty, gold-hungry invaders of South America when I think of emeralds. They terrorized the native populations, tortured, enslaved and slaughtered them, and once they had their booty on heavily loaded ships, they were hunted by pirates themselves. Often those overloaded ships went down in hurricanes in the Caribbean. Some truly amazing emeralds have come up with divers to those galleons.