Grandidierite is one of the rarest stones on earth. The more transparent the clarity and the more vibrant blue to green, the color the more the gem is worth. They command very high prices (over 50,000.00 a carat for fine color transparent gems of larger than 3 carats) when they are gem quality (high clarity and excellent cut and color).
This extremely color saturated grandidierite in unusual due to being such an incredibly deep teal. This gem is translucent like jadeite. If it were transparent it would sell for well over 50,000.00 a carat. A recent discovery has made grandidierite temporarily available, but beware of fakes and buy while you can since when the mine plays out it may be unavailable again for a very long time and prices will again rise steeply.
Translucent gems that look like blue or blue-green jadeite are also very coveted and sell for a lot of money. Often dyed, treated, or faked you should know your dealer.