Brushtail Codex

Gemstone Golems are the rarest type of golem to wander the planet and can produce cataclysmic amounts of damage if they find the surface.

Their bodies are as strong as obsidian and have untold resilience due to their construction.  It takes centuries of magic and earth under extreme pressure to birth one.  These monsters are usually found in depths that most normal people cannot survive.

Gemstone Golems usually require armies to subdue and any sane group of adventurers will tell you it is suicide to go looking for one.  

Rumors state there is one sleeping within Dragonflame Mountain, which is why many adventurers don't go near Dragon's Maw.

The most infamous one in modern times was located in a derelict, but mineral-rich asteroid in local space.  It took the full force of the Brushtail Brigade to take it down.  As a reward, the Brigade took the asteroid for themselves which became the Grand Mining Facility.