After your second run through the mines, temporary power ups will be available. They will fall into your mine cart like a gem, but are not activated until you break them out of their rocks. To do this, match gems that are next to the trapped power up. The power-ups each have a specific function.

Diamond Rush: Spawns a number of diamonds for you; most useful power-up.
Double Multiplier: Temporarily doubles your current level multiplier; useful to get high scores.
Jackpot: Temporarily doubles coins earned from each gem.
Rocket Cart: Mine cart moves quickly forward for a limited time, all gems immediately destroyed once touched, points are lower than normal, combo multiplier limited to 3x maximum; least useful power-up.