There are several types of gems in the game:
- those what are part of the dungeon puzzles, and you have to use them to open doors, by inserting them into empty eye-sockets in reliefs on walls
- those what you can add to sockets to your items to give bonuses, like critcal chance, etc
- and that blue gem which is a currency that can be used to buy stuff, for example inventory or storage spaces, and it costs real money, so by purchasing it, you can support the developer
