What is best place to have an Amethyst stone certified as Being Natural. Does GIA certify and what it costs?

Answer 1

The GIA does not certify coloured stones. Your best bet is to take it to a reputable jeweller as it is a very easy stone to identfy when you have a little experience.

Answer 2

Only diamonds are GIA certfied, not amethyst stones.
The advantages of buying a diamond with a GIA certificate are:
You will know exactly what you are buying. Every important factor you need to know about the diamond is described in the certificate.
The seller knows exactly what he/she is selling to you so as to avoid any misunderstandings in the future.
If a diamond comes with a GIA certificate, you do not have to worry about the possibility that you might be purchasing a fracture-filled diamond. These are diamonds that have surface cracks that can be artificially filled to appear as much better diamonds than they actually are. These are in essence, very low quality diamonds that look great to naked eyes. GIA does not certificate these diamonds.
If a diamond comes with a GIA certificate, you will not become a victim of buying a synthetic diamond. Yes, there are real man-made diamonds that hit the market in 1977. Currently, average jewelers have no way of telling if a diamond is natural or man-made (These are not diamond stimulants as CZs, but real diamonds that are man made).
Purchasing a GIA certified diamond will simply provide you with much more confidence and value.