Blue or greenish beryl. Most stones are pale to medium bluish-green, as the name "sea green" implies, but they are almost always heat-treated to enhance the blue coloration.

 This heat-treating results in permanent color change and duplicates natural heating that occurs in areas of volcanic activity. Aquamarine often occurs in very large sizes, usually with very good clarity.

 Brazil is the largest source. In recent years, the price of aquamarine has declined somewhat, as an abundance of inexpensive blue topaz look-alikes has flooded the market, but large, fine aquas are still highly prized.