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Obscure Burglary Tools of the Day: Ninja Rocks

Posted in Parking, Politics, Tips by Vito Rispo | July 25th, 2008 | 41 Responses |

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:

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41 Responses

  1. Adam says:

    Actually, this works with even smaller pieces of ceramic. I worked as a mechanic and one of the other mechs told me that insulation from a spark plug would break glass.

    We had a spare window so I crushed a spark plug and picked up a “wafer” for lack of a better word the size of a paper hole when you punch a piece of paper.

    It burst the window quietly and perfectly. I threw it very hard but it was so light I didn’t think it would work.


  2. Benj says:

    I was trying to figure out why someone keeps breaking the spark plugs on my kz650 and came across this:
    …talks about positive and negative charges as to why that works. I wonder who’s story is right.

  3. Devon says:

    Dude, thanks for the tip I was trying to figure out how to mug a house and the first thing that actually stopped me from doing it was the how to enter the house without alerting the neighbors. I tried on finding an unlocked window or door but all were perfectly closed. Then I tried on busting the window on the kitchen with a hammer but it would eventually make a hell of a noise and alerte the neighbors…
    I hope I can use spark plugs or ceramic to smash the window. Thanks

  4. Accomplice4hire says:

    If by any chance you have not ‘mugged’ that house yet, let me know where and when you are going to do so. I have been looking for a house to target for a while now. ;)

  5. John says:

    Devon your comment should flagged. I can’t believe you’d even admit to breaking into a house and post it on the web you moron. I hope you get caught and get charged with breaking ‘n entry and burglarly.

  6. Jeff says:

    @John you got trolled.

    As for this posting, excellent, thank you! Some a-hole tried to steal a spark plug out of my CB750 (damaging the fins in the process, the prick). I’d read that they used the ceramic to smoke crack out of, which didn’t really make much sense to me…

  7. j says:

    breaking and entering sucks but, John, do you think that Devon could possible be joking around? get over yourself.

  8. David says:

    John your comment should be flagged. I can’t believe you lack the ability to understand jokes and sarcasm and then post it on the web you moron.

  9. Joe Bee says:

    Or mayube John’s comment should be flagged for a missing sense-of-humor.

  10. zane says:

    @ John

    he was obviously just kidding…..chhheeeeeiiiiiilllll

  11. Wisedome says:


    I was going to explain sarcasm to you but I have better things to do.

  12. cephyn says:

    Wait, so a brick won’t break glass, but the ceramic will? and yet you can break the ceramic with….the brick?

    does that not strike anyone else as a little odd? brick > ceramic > glass > brick?

    something else is going on here.

  13. Chris says:

    Cool, going on a crime spree after work.

  14. Guywho'snotgoingtomugJohn says:

    @Devon @Accomplice4hire Keep it on the DL, but I know where John lives. I’ll send you the details and we can do it to it. Evenings work for you?

  15. Jexie says:

    So if the ceramic is much harder how come the brick can break it but not the glass?

  16. Nemo says:

    John, you’ve been trolled. Welcome to the internet, you’re obviously new.

  17. Dave Daurelle says:

    Hardness and brittleness are measures of two different things. It’s very common to find hard (mohs scale) things are more brittle than soft (mohs scale) things.

  18. rep says:

    Watch the mythbusters episode where they simulate a car being driven into water and show the best way to escape. They explain how the safety glass works and why its so hard to kick out the windows while your sinking. They even show two over the counter windshield breakers. Its neat stuff.

  19. YoDawgIHeardYouLikePhysics says:

    The ability of ninja rocks to break glass has little to do with hardness. If this was the case, you could use any unbroken piece of ceramic to get the job done. The reason it works, as demonstrated in the video, is because he broke the spark plug.

    Ceramic like that in a spark plug shatters along very fine lines. This produces a fine edge, that will break the window far more effectively than a giant brick. The brick doesn’t do anything because the thing is heavy, but blunt.

    Hardness certainly counts for something, but it’s not the main force at work here.

  20. DixieNormus says:

    @ cephyn
    We should change the game “Rock-Scissors-Paper” to “Rock-Spark Plug-Glass”

  21. Chris R. says:

    I think you’ve *all* been trolled.

    I wouldn’t doubt that the pieces of ceramic could scratch or crack the tempered glass, for the reasons stated. But breaking the glass apart like that requires energy, far more energy than human arm muscles could store in a small piece of ceramic by throwing it.

    Further, I guarantee the brick contains plenty of minerals that have a higher hardness than the glass. The common way of testing this is by scratching. If you can scratch the glass with the brick, the brick is harder than the glass (just like the ceramic).

    I call bullshit on the video.

  22. D says:

    Try it Chris R., it’s real. I’ve seen bricks thrown at side windows on cars and take more than one toss. Those little pieces break shit.

  23. Clemoh says:

    Don’t be too quick to call bullshit. Bricks, are after all an aggregate substance, and one of the elements, crushed stone, might be hard enough to scratch glass, but not the clay that makes up most of it. The object doesn’t have the density of it’s hardest constituent.

    Actually folks, any old ceramic WILL do. When I was a young punk about 25 years ago in NW Ontario, we used to go robbing cars for beer money, and used nothing but a coffee mug and 3 feet of rope tied to the handle. You just give the coffee mug a few quick swings and launch that sucker through the car window. it only works on safety glass, but it destroys the window without making much of a noise.

  24. […] Obscure Burglary Tools of the Day: Ninja Rocks (tags: science ninja diy glass rock Mohs scale ceramic) […]

  25. mur says:

    Heh, I think John’s the troll here – he’s the one that got the biggest reaction.

  26. S.o.G. says:

    @ Chris. R.

    Why don’t you try it? What are you some kind of christian? Who automatically believes that whatever answer pops into their head is more valid than reality?

    And to answer your question, the answer is the energy is in the glass. Tempered glass contains potential energy. That’s how it works. Tempered glass is made by processes which create balanced internal stresses which give the glass strength. But you know, god forbid you would take 15 seconds to actually look something up before assuming your first opinion is the right one.

  27. RichardCranium says:

    @ Chris R.

    I’m pretty sure science just trolled you. “A higher hardness” … really scientific terminology there.

  28. dan says:

    maybe john trolled all of you?

  29. Some guy says:

    @ Chris R.
    I thought that glass like this was designed to shatter into small pieces once broken, as a safety feature. Not entirely sure, but I imagine having a huge sheet of glass fly at me in a car accident would be much worse than many small pieces. The ceramic just needs to be sharp and hard enough to begin the breaking.

  30. jtran says:

    @ Cephyn
    its like rock paper scissors

  31. clarity says:


    The glass is under stress to make it harder and to break into tiny pieces that will not cut you in an accident. how it works – glass

  32. Turdburglar says:

    To all those who think John got trolled, LOL YOU all got trolled by JOHN! He was just lolling around lollsers, ‘sif he didn’t get the joke LOL, oh and also… LOL!

  33. Vito says:

    @Chris R

    Try “scratching or cracking” tempered auto glass (any glass except the windshield, which is laminated) without it breaking. Side and back windows in cars shatter, they don’t crack or scratch. Any damage enough to cause even the smallest crack will “pop” the entire door glass, they’re made that way to avoid slicing people up in accidents. Honestly, I’ve tried this; it really works. Really.

  34. Jeff says:

    Someone should send this to the tv show, TIMEWARP. Maybe it would make more sense when slowed down…

  35. […] 7, 2009 Obscure Burglary Tools of the Day: Ninja Rocks – “Ninja rocks are small bits of the ceramic from spark plugs, used by crackheads and […]

  36. […] Sources: – Wikipedia article on Ninja Rocks – Wikipedia article on tempered glass – Wikipedia article on spark plugs – Wikipedia article on Mohs scale – Article from Ride Lust on Ninja Rocks […]

  37. […] of spark plug on there would actually break the car’s window, which reminded me of something another friend wrote about a burglar tool called “ninja rocks.” Check out the video of a ninja rock vs a […]

  38. isaac says:

    if ceramic is so hard, im confused as to how its so easy to break the spark plug?

  39. […] more information, consult your local crack head, or visit this site here for a detailed write up from a victim of Ninja […]

  40. who cares says:

    sometimes it takes two pieces to break i always lick th sparkplug first its easier