Given the advanced technology of the Ancients, I'm assuming that the windows in Atlantis are more than simple glass. And I'm pretty sure there were instances on the show where bullets ricocheted off the interior windows without harming them. However, when infected with the Iratus Bug virus, Sheppard shattered one with a single blow - after which, it appeared to shatter into small fragments like tempered safety glass would. I'm guessing, though, that it is supposed to be some sort of futuristic Lantean polymer material.
Has the show ever mentioned what the windows and "glass" of Atlantis are made of, or even just a mention of what the Ancients used instead of glass?