Why does Dragon Glass kill White Walkers?

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Tags

1. #works
2. #defend
3. #steel
4. #shattered
5. #discovered
6. #first
7. #stabbed
8. #dragonglass
9. #against
10. #greater
11. #themselves
12. #glass
13. #tarly
14. #white
15. #killing
16. #potential
17. #walkers
18. #after
19. #volcanic
20. #sword
21. #supply
22. #valyrian