Dragon Glass!!!

In case anyone wonders why my recent obsession with obsidian aka dragonglass, and also why I think that tossing it into the mouth of one of the walking dead (as I suggest here
https://www.etsy.com/listing/103488257/pendant-necklace-caged-apache-tears )
may work, here's George R.R. Martin in A Storm of Swords (Vol. 3 of A song of Ice and Fire) on what happens when the "Others" (the walking dead) come in contact with it.
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He heard a crack, like the sound ice makes when it breaks beneath a man’s foot, and then a screech so shrill and sharp that he went staggering backward with his hands over his muffled ears, and fell hard on his arse.

When he opened his eyes the Other’s armor was running down its legs in rivulets as pale blue blood hissed and steamed around the black dragonglass dagger in its throat. It reached down with two bone‐white hands to pull out the knife, but where its fingers touched the obsidian they smoked.

Sam rolled onto his side, eyes wide as the Other shrank and puddled, dissolving away. In twenty heartbeats its flesh was gone, swirling away in a fine white mist. Beneath were bones like milkglass, pale and shiny, and they were melting too. Finally only the dragonglass dagger remained, wreathed in steam as if it were alive
and sweating. Grenn bent to scoop it up and flung it down again at once. “Mother, that’s cold.”

“Obsidian.” Sam struggled to his knees. “Dragonglass, they call it. Dragonglass. Dragon glass.”
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Need I say more?