Emerald is a specific type of green beryl colored by vanadium and chrome. Emerald, unlike many other gemstones, is prized for it's inclusions or "garden" within the gemstone.
First known emerald mines were in Egypt dating back to 330 B.C. The Incas have been using emeralds since around 1100 A.D. in ceremonies and rituals.
Emerald was believed to be a color of green that would relieve eye strain if gazed upon by the ancient Romans. Now, gazing upon high quality emerald can lead to wallet strain.
Emerald is an 7 on the Mohs scale of hardness, so the same as a quartz crystal making them a good choice for jewelry.
Emerald is the birthstone of May.