To apply a fairly abstract curiosity to the contents of your pocket, it is closely related to Gorilla Glass[tm]. Gorilla Glass is chemically treated "tempering" rather than heat treated.

Ref: http://en.wikipedia.org/wiki/Gorilla_Glass#Manufacture

http://en.wikipedia.org/wiki/Toughened_glass#History

This is true of all tempered glass, not just that dropped in cold water. The side windows of your car can do the exact same thing because tempered glass is under stress and, when something comes along to break it and release all that stress, it explodes just like the sample pictured in the article, which is why we have to cut and seam it before tempering it. (Your windshield is laminated. Having it blow up like that sample pictured--a very real possibility--could easily cause an accident.)

Normally you don't see windows explode because the edges are smoothed before tempering and protected inside a frame. But if you happen to have a piece of tempered glass and nick the corner against something, it will probably blow up. Actually, tempered glass occasionally blows up all on its own, usually during winter, but you probably won't see that unless you've worked for a cut & temper operation.

If you want to know a lot more about this, take MIT's 3.091x (Introduction to Solid State Chemistry) from edx.org. It's quite a fun course.

I like a glass of cold wate on occasion.

"cold wate"