Gems can be found with the Gem Finder bought in the shop after getting the Community Center.
Basic Gems Edit
|Gem Type||Rarity||Expected # of
Days to Obtain
|1/500,000||5.79 Days||This cannot be sold|
Every Gem (except blood crystals) will upgrade tools in the order above. You need to be global level 1500 and buy the ability to socket blood diamonds for 100m to be able to upgrade tools to blood diamonds. Upgrading tools is much more valuable than selling them to the NPC market, but trading them can give you some quick cash.
If you have T5 mining, every gem can be upgraded to the next gem if you have 10 of that gem. This works for every gem except Blood Crystals and Blood Diamonds.
Note: Blood Crystals can only be mined if you have T3 Mining.
Another Note: Selling gems is not recommended, unless you are trading as people would buy them for 1000 to 2000 times more than the NPC.