Note: This post talks about dragonglass, which may reference various episodes in HBO's Game of Thrones (GoT). The only content that's discussed in this OP is directly related to dragonglass, which includes any conversations/events that may directly involve/mention dragonglass.
From what I understand, dragonglass is obsidian. My question is, does GoT ever actually mention why this glass is effective against white walkers? Is it solely because obsidian is made at high temperatures by volcanoes (with White Walkers being "ice-like")? Or, does it have to do with the origin of White Walkers, with respect to the Children of the Forest?
A long-forgotten secret is that the Children [of the Forest] actually created the White Walkers as a weapon, by transforming humans into them: this was achieved in a magic ceremony that involved (among other things) plunging a dragonglass shard into a human's chest.
Perhaps, due to the ceremony involving dragonglass, the White Walkers now have a negative affinity towards it?
Aside from these two theories, I've got nothing.. can anyone help in explaining this?