The emerald is a gemstone for Mercury. Some points relevant to this stone are as under.
[13] SIGNS OF HIGH QUALITY EMERALD
A high quality emerald will be:
(1) Of a bright green colour.
(2) Of a high density.
(3) Delicate.
(4) Slippery.
(5) Smooth.
(6) Glistening.
(7) Shining.
(8) Sparkling.
(9) Reflective.
[20] SHAPE OF EMERALD for wearing
A person should try to wear a rectangular or square shaped Emerald.
If possible one has to try to wear an emerald that has been cut according to "emerald cut". (Which is considered to be the best).
A person should also try to avoid round shaped emeralds.
For the remaining 23 points, you can contact us or you can refer to our book “Astrological Science... Your Birthstones and You".