The stone he put in its place looked almost exactly like Jon's stone, but it wasn't. Sure, it worked in every way like the original stone, but it also held within it a destructive curse that would bite the bearer of the rock using their own words against them.
This was one of the many mythical Wordstones, a concept born a long time ago in the world of the Fae, where words are power and every promise a deadly contract.
The particularly nasty Wordstone placed in Jon's possession was the...