Coralstone is a rock-like material built up over time by from sucorolith reefs. It is chemically similar to limestone, being made from the compacted shell-like structures of virid sucoroliths.
Coralstone makes an excellent building material, since it is strong but incredibly light, being a honeycomb of strong tube-like structures. In the Jade Epoch the coastal Issid civilisation built their distinctive towerhouses from large blocks of coralstone, hence they were called the Issid Block States by later archeologists.