Emeralds are medium to dark green; the most valuable stones are pure green with no tendency towards yellow-green or blue-green. Emeralds are the birthstone for the month of May.
The most popular cut for an emerald is an Emerald Cut, since this cut will minimize stone's weight loss in the cutting process and allows more light to come through the stone to make it more beautiful.
Emeralds are sometimes treated with oil to fill their fractures. These fractures are a characteristic of emeralds, and this treatment is an accepted procedure in the jewelry industry. You should never clean an emerald in a heated ultrasonic cleaner. This will either fracture the stone or cause the oil treatment to be removed or damaged. Do not clean an emerald yourself -- take it to a jewelry store. Make sure emerald is handle gently and avoid heat.
It is rare to find an emerald that has not undergone treatments to enhance color and fill cracks. This has become a standard practice in recent centuries.
Emeralds are sometimes irradiated for clarity.
The following are terms for fake emeralds: "African emerald," "Cape emerald," "Evening emerald," "Indian emerald," "Medina emerald," "Mt. Saint Helens emerald," "Spanish emerald," "Scientific emerald," "Synthetic emerald," "Zerfass emerald," "Uralian emerald". (There are probably more terms for non-natural emeralds that we have not yet encountered; please write us if you are aware of other or new terms.)