Portal

Oh man, I could talk quite a bit about science!  

Just today (er, yesterday) in my mechanical properties class, we were discussing fractography when we started talking about Prince Rupert’s Drops.

What are those?  Well, they’re basically little tear-drop shaped pieces of glass.  They’re incredibly tough, but if you snap off the tail end of the teardrop, the rest of the drop violently explodes due to how stressed the material is at the atomic level.

Video link!  There are a whole lot more besides this, but this is one of the ones we watched in class.

TL;DR - really tough glass that you can hit with a hammer, but if you snap a tiny piece of it off, it quite literally explodes.

Also something interesting: Cracked.com ran an article a few days ago about some really cool materials.  Go check it out!