Silent Stone is a type of stone that is able to nullify the abilities of Silvers and Newbloods.
Background
Silent Stone is made by mixing blood from silences, such as members from House Arven, with concrete.
The Kingdom of Norta builds their prisons to house Silent Stone cells so that their prisoners cannot use their abilities. Silent Stone in large quantities can slowly make a Silver or Newblood uncomfortable and weaker, and it may even kill them over long periods of time, requiring that a guard walks the prisoner in order to keep them alive. Silent Stone is also fashioned into manacles.
People affected by Silent Stone can slowly adapt to it, as the power exerted by it is constant, while a silence's silence can strengthen from concentration. In King's Cage, Mare slowly trains herself so that she can have increasingly more stamina while wearing the Silent Stone manacles.
Silences, such as those of House Arven and Cameron, are not affected by Silent Stone.
Silent Stone can also be used as a sort of protection, as abilities cannot affect someone who is wearing Silent Stone manacles or near a large amount of it. Maven used this to protect Mare from the pain ability of Prince Alexandret, and he himself sits on a throne made of Silent Stone to protect himself from the whispers of House Merandus.
The Kingdom of the Rift is currently producing Silent Stone by slitting the wrists of Arven silences and having Wren heal them and stimulate their blood production to start the process again.