You watching it suspiciously for a while made me laugh.

The cracks were just due to the glass trying to contract, I would imagine. Unless there's another reason and we can both be ensmartenified and edumacated together.

I totally blew up an egg in my microwave once. I am talking major bomb explosion blowing up. Egg everywhere, broken microwave. This was years ago. I now know you don't boil eggs in a microwave.

To my knowledge most "ordinary" glass will do that when exposed to a sudden extreme temperature change. Borosilicates like pyrex don't--that's why you can bake with pyrex.

Also, I think your water superheated and then went from no boil to full boil in an instant. The things you learn in chemistry class...

Any time you put cold water in a hot glass, you're risking cracks. I've seen it happen when making lemonade in a pitcher fresh out of the dishwasher, and I've heard of pyrex pot lids shattering when placed in a sink with a tiny bit of water. I, myself, was victim to an exploding lightbulb over a bathroom sink, when a droplet of water from my freshly-washed face hit a hot bulb.

I'm pretty sure that someone attacked you using their psionic ability but the glass took the brunt of it. Be careful.

Didn't you watch Alien 3? Hot to sudden cold = CRUSHINATION.

I bring water to a boil in the microwave sometimes and haven't this happen. I use a heat-safe mug or glass. Usually about 2 minutes is enough for a cup or so of water. I'd be surprised if your water could have boiled so explosively. Was the glass covered so that pressure built up?

Thanks for the SCIENCE, people. Especially craniac-- that makes the most sense.

Dark Forest-- it was uncovered. Dunno why I felt the need to vaporize the water.

And I haven't seen any of the Alien movies, brownpau.

Or the Godfathers.

So, this thread has now established that I'm both stupid and uncultured. Well... I bet I could beat anyone on this thread at 8-bit Nintendo Ice Hockey, though.

What happens is this: Water needs nearby air (bubbles), or very high temperature (a kettle's metal wall on a regular stovetop) to change from liquid to vapor. If there are bubbles on the water when you put it into the microwave, these bubbles will start the vaporization, and the water will boil as normal. If there aren't bubbles (e.g., still water on a glass container), the water in the bottom of the container won't immediately vaporize, but reach a few more degrees over boil point. Then, when there's some perturbation, a lot of it vaporizes at once, causing that explosion. If you want to boil water on the microwave, either make sure it has a few bubbles sticking on the glass walls, or put a toothpick inside (which is wooden and will provide bubbles).

(Yeah, this happened to me once, and I was creeped out and researched it)

Also, once my friend was drinking juice from a glass, and when he put it down, it literally blown to pieces (a lot of pea-sized pieces). No one was able to explain that one (it was cold juice, the surface was cold, and the glass wasn't washed in hot water).

When I was little, I saw a glass explode in my mom's hand when she pulled it out of the hot, soapy water and rinsed it with cold from the tap. Cut her up pretty good. Freaked me the hell out and is one reason why I will always always have a dishwasher.

Yup, eamondaly, that's exactly why I had to take my stepson to the emergency room some years ago. He took a nice, hot, clean glass from the dishwasher and filled it with milk. Keerash. Took about four stitches to close the gash in his thumb.

Needs more than just a hot surface. It needs a rough surface on which bubbles can form (not unlike a seed crystal). Second the toothpick or a bamboo skewer.

Yep, the water superheated. The Urban Legends Referenced Pages (snopes) says that superheating in the microwave is "True, but rare."

I don't care what Snopes says, I say get Adam Savage and Jamie Hyneman on for The Case of the Exploding Water in Microwave.

If it makes you feel better, a friend of mine started a fire in his microwave once. No clean socks, other than the ones on the drying rack, so he popped a pair in for 90 seconds.
Bad move.