- Boulderax - Green Crystal
- Firox - Red Crystal
- Glaciator - Blue Crystal
- Meltrox - Orange Crystal
- Sulfurix - Yellow Crystal
Rock Monsters are bipedal semi-humanoid creatures, with a grey, stone-like head that flips upwards when it opens its mouth, and black eyes with red jagged pupils. The Rock Monster body is a transparent crystal colour (each creature has its own colour as noted above), with grey stone covering some of the outside of it. They glow from within with an internal light the same colour as their crystal.
Rock Monsters will wander around when idle, growling and raising their hands while opening its mouth very wide. They will freely enter the water, walking on the bottom with no need to breathe.
The Rock Monsters are the enemy of the Power Miners (Duke, Brains, Rex, and Doc). They appear in most of the Power Miners sets. They are made of different coloured rock and crystals. There are five different kinds of Rock Monster. Meltroxes are red, and are apparently always angry. The yellow ones, Sulfurixes, are more intelligent and can melt tunnels through solid rock. Apparently, all of the Rock Monsters are afraid of the blue Glaciators. The Glaciators are shown to have ice powers (as seen in the trailer for the game Rock Rocket). The green ones are Boulderaxes which are strong, slow, but not intelligent, and often attempt to destroy the Power Miners' vehicles. The orange ones are Firoxes which are extremely fast, sneaky, and love to play tricks.
According to the LEGO Magazine the Rock Monsters have been tunneling to the surface of the Earth so they can take over the LEGO World after mysterious earthquakes from deep in the Earth, and the Power Miners plan to stop them.
- Glaciator was the first released, and only Power Miners-related content until after Early Access ended. It was also the first translucent character or creature.