Ninja rocks are small bits of the ceramic from spark plugs, used by crackheads and jerkoffs to break any of the tempered glass on a car (anything except the windshield). Usually the door glass.
All your average crackhead needs to do to make some ninja rocks is to find a spark plug and smash the ceramic insulator part into about 1/2 to 1/4 inch bits. Then they just need to throw them at a car door glass and steal the 2 dollars in quarters and red Phillies hat from off of my seat while I’m eating Pho in the Vietnamese place. I hate crackheads.
What makes the whole thing so bizarre is that the ninja rocks don’t feel like they could break anything, they’re extremely light. A rock of similar size off the ground wouldn’t do it, but ninja rocks do. Why?
It has to do with hardness. Glass is actually “harder” than iron on the Mohs scale, and spark plug ceramic (technically called “aluminium oxide ceramic”) is much harder than glass. Aluminium oxide ceramic actually rates a 9 on the Mohs scale; diamonds are 10, glass is 6.5, and iron is 4.5. That’s the key to the whole thing, and why it’s surprisingly hard to break a window with a hammer and surprisingly easy to break it with a small, light little shard of innocent white spark plug ceramic.
And so, in conclusion, ninja rocks are interesting, and the next time you see a freaky little crackhead running around Philadelphia with a red Phillies hat and a bunch of broken little ceramic shards, run him over once for me.
Check out this video I found on ze interweb: