Sending Stones

While you touch one stone, you can use an
action to cast the sending spell from it.
The target is the bearer of the other stone.
If no creature bears the other stone, you
know that fact as soon as you use the stone
and don't cast the spell.
Once sending is cast through the stones,
they can't be used again until the next dawn.
If one of the stones in a pair is destroyed,
the other one becomes nonmagical.