There is 7 types of gems and i will talk about how valuable are a little bit and why they are used. I mysels usualy keep 1-2 low level gems of every type on mule just in case. Generaly speaking people will want to buy Perfect games, sometimes you could even sell Flawless gems, lower qualities are wanted only rarely. can be used for rerolling magical items (usualy Grand charms).can be used in many different recipes in Horadric Cube.can be used to craft Rejuvenation potions.Gems are generaly used for several things: I am very busy playing D2R myself so consider this being under construction
I will start very simply and talk about Gems and next update will be Runes. Ok thats probably all, Now I would like to talk about prices and how to know what to keep.