It is connected with planet Mercury. The metal it is associated with is gold. It rules over central nervous system, lungs and skin. It can be worn by those whose ascendant is Taurus, Gemini, Leo and Virgo. It is to be worn in little finger.
Emerald jewelry is said to strengthen the nerves and, on the physical side, to purify the blood. Emeralds increase the flow of positive life-energy and are used by healers to further increase their own abilities to heal the body and mind. Like hessonite and ruby rings, emerald rings and pendants should be designed so the gem is in contact with the body.
Emerald is also recommended for strengthening the planet Mercury, which increases the powers of communication. Obviously this is important and necessary for business people and those in the various fields of communication, be they writers, speakers, or entertainers. Most people would further agree that our quality of communication is 90% of the determination to succeed in whatever endeavor we may wish to undertake.
Emeralds generally have many imperfections and most jewelers would say that these flaws insure a "natural" stone. For healing purposes even emeralds should be fairly "clear" to the eye. Some imperfections are not harmful nor impede the stone's vibration and an experienced planetary gemologist knows which are or aren't permissible.
Sources of emerald are South America, most notably Colombia and Brazil, Africa (Zambian and Tanzanian are best), India, Iran, Pakistan, Afghanistan, Egypt and Russia.
Green tourmaline is the best substitute for emerald although the potency is somewhat lesser than the primary stone emerald