Seriously, i just stuck a pizza in the microwave for 3 minutes on high to microwave my pizza... and my plate broke nearly in half!

The funny thing was the cheese on the top wasn't even fully melted... the bottom was cooked well though... weirdest thing.

Normally I drop the microwave on the plate. In you're case, I don't know. Maybe some moisture got trapped inside of the plate when it was made.

I've had the plate for like.... years though.

Even used that plate in the microwave plenty of times before.  Infact for like a minute earlier in the day before doing the dishes...

I don't know about porcelain in particular, but lots of ceramic and glass items do not respond well to being unevenly heated; and the microwave doesn't provide even heating. This doesn't mean that these items will break the first time (or in the first 1000 times) you heat them this way, it may require the uneven heating to be just-right to put pressure in a flaw that has developed (or possibly always been there) to crack/break the item.

Yeah. I had a drinking glass explode in the microwave, years ago. They aren't exactly "microwave safe".

Actually I don't know if it's even porcelain... it's just... whatever plates are made out of.

Damn, how do you find an actual microwave safe plate if that's the case....

Is your microwave plate rotating? Because uneven heating (as Happysquirrel beat me too *shakes fist*) can cause a porcelain plate to crack. If the plate wasn't rotating then it would have been heated unevenly. It could have happened through temporary obstruction or a broken motor.

Makes sense actually.  The place i moved into had a microwave but the rotater is broken.

Then I would imagine that a broken rotator is most likely to be the reason it cracked.

That's why I respect highwaystar. He brings the lulz, but the guy really knows his stuff.