From Sagan 4 Alpha Wiki
The tomb crystal replaced its ancestor the obelisk crystal in the Somarinoa Coast. Due to the tropical weather and more sunlight the obelisk crystals in this coast could grow twice the size their ancestors did and as time passed by became a unique species. They have evolved a unique shape that resembles a sarcophagus or a tombstone. They still have an outer later of poison to protect them from predators.