Chemical composition -- Beryllium aluminum silicate. Relative amounts of additional metals give rise to the different color varieties.
The beryl family provides many well known gems.
Color -- Very wide color range.
Optics -- R.I 1.58-1.59, varying with the composition.
Durability -- Hardness 7.5-8.
Crystal structure -- Hexagonal.
Specific Gravity -- 2.66-2.9, varying with the composition.
Sources -- Very widespread. Some of the major sources include Colombia, Brazil, Madagascar, Zimbabwe, and Zambia.
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.
Colorless beryl. Abundant and low priced.
Light to medium green (not bluish) beryl. Lacks the intensity of color to be called emerald and subsequently commands lower prices.
The rarest of beryls, found only in the Wah Wah Mountains of Utah. Always quite small, usually under 1 carat, and correspondingly expensive. At least one dealer has attempted to market red beryl as "red emerald," but most are unwilling to accept that appellation.