Gemstone 1: In the first chest box near the slugs.
Gemstone 2: Defeat all three Fire Turtles.
Gemstone 3: In the box next to the switch that activates the crushers.
Gemstone 4: In gem cart near were the mine carrying cart that takes you out is located.
Gemstone 5: In boulder. To get out, turn on crusher, put the boulder under it, and turn the crusher switch.