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. The rock monsters are Meltrox, Boulderax, Glaciator, Sulfurix, and Firox. 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.
They are shown to have some primitive technology, like catapults. The Rock Monsters eat crystals, which give them power. If a rock monster eats a different coloured crystal to what it is it will burp and break wind, according to the video released by LEGO Club TV on YouTube. If they consume dynamite (and it goes off in the stomach) they will apparently solidify.
In Summer 2009, a new type of larger Rock Monster was released. They appear to be larger versions of the small monsters. The large version of Sulfurix is called Geolix, while the large version of Meltrox is Tremorox. As well as those, another rock monster called the Crystal King or Rock Rage was released in May 2009 as the biggest Rock Monster. He is now awoken from his sleep.
Rock Rocket is a game on LEGO.com. In it the player controls a rock monster and lets him eat crystals.
- In 2854298 The Adventures of Clutch Powers, the little ones as seen in early 2009 are referred as a "Baby Rock Monster."
- The throw monsters are seen as orange creatures in Ninjago: Masters of Spinjitzu.
250px|thumb|left|The Power Miners Teaser
|view · talk · editPower Miners minifigures|
|Power Miners:||Brains | Duke | Doc | Rex|
|Rock Monsters:||Boulderax | Firox | Geolix | Glaciator | Meltrox | Sulfurix | Tremorox | Crystal King|
|Lava Monsters:||Combustix | Eruptorr | Firax | Infernox|