Collect gem mines and gem tokens to be able to buy more mines. Higher value gem mines can give more victory points. The first player to reach 15 VP wins, although all other players will have 1 more turn to try and score higher than 15.
On a players turn, they can either buy mine, or collect gems. If collecting gems, you can either draw 3 different gems, or 2 of the same gem. Be wary though, you can only ever have at most 10 gems. If buying a mine, the gemstone cost to buy the mine is lowered by however many mines of each gem cost that you already have.
For example, lets say you already have 2 sapphire mines and 1 ruby mine and you have 2 sapphire gems and 2 ruby gems. Now you want to buy a mine that costs 3 sapphires and 3 ruby gems. You have 2 sapphire mines, so the effective sapphire cost is only 3-2=1, so you only spend 1 sapphire gem. For the rubies, you would need to use both your ruby gems because you only have 1 ruby mine.