Dragonglass

The man screams in agony, and when Leaf is done inserting the dragonglass, his eyes turn ice blue.

While they struggled to reach an amicable solution, their meeting would prove to be fateful for both characters, while Daenerys' accepting Jon's wish to mine dragonglass on the island was a decisive show of goodwill.

The shot that shows the contrast between the glowing red crucible and the blue of melted dragonglass couldn't be a clearer reference - but is it an important one?

The weapon Arya commissioned from Gendry (a double-sided spear with a detachable blade) is also made of dragonglass, suggesting Arya hopes to get up close and personal with the White Walkers.

Dragonglass’ official message board is medium.

I'll trade my dragonglass for two wool, please.

She needs the support of the beloved King of the North, while he needs the dragonglass in her caverns and the support of her armies for the impending wight war.