Gem Stones
What it is? Its pretty much a better version of gold bars that sells for more, but it has a rating system.
The better the gem stone is the more it sells for, and to make gems stones they can be building in the hideout that makes this. And the chance to get better gems stones are low, and the higher the level the building is, the higher the chance to get better gem stones. The buildings can be called Gem Mines. Having that bad quality gems are common and good ones are very rare.
The value of it ranges based on its purity:
Cracked
Translucent
Normal
Partially Flawless
Flawless
Some people will say this is meaningless if i leave it like this.
So,
Uses : For level upgrade on all hideout building at level 5,10,15,20
Possible Uses,
To make expensive ships like SOTL, LF and so on.
Also, Country can make the port it is controlling don't allow someone to sell them. If you do sell them, you will gain hostility towards that nation, same goes for buying.