Something this author just found out is that Emeralds and Aquanmarine are both varieties of beryl? Pure beryl is colorless, however when it is formed if it reactes with specific chemicals it can drastically change colors. In this case the March birthstone the Aquamarine it becomes a idyllic blue hue when it interacts with trace amounts of iron in the formation process.
Emeralds are formed in the same way but the classic and sought after green color is created when miniscule amounts of chromium or vanadium meet the colorless beryl in the formation process. It is that combination that makes the great and highly desired green hue. It is not known for it's strength, however as it scores a 7-8 on the mohs scale.