Elfstone

A type of building material invented by the High Elves of the Old Empire. Elfstone is incredibly smooth and ever so slightly translucent. While it comes in many different colours, greens and dark reds are the most common.
The secret of making Elfstone was lost with The Ruination, but somehow rediscovered by the great Irilianer architect Karol Stonemannen. Examples of buildings either made entirely out of Elfstone or with significant Elfstone elements in Sigsland include Tor Wysard in Irilian and Haero's Wall.