# Hardness of kidney stones **URL:** \ **Category:** Factual Questions\ **Created:** [March 18, 2013, 10:18pm UTC](https://boards.straightdope.com/t/hardness-of-kidney-stones/653305 "2013-03-18T22:18:52Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Reyemile](https://avatars.discourse-cdn.com/v4/letter/r/46a35a/32.png) [@Reyemile](https://boards.straightdope.com/u/Reyemile)\ **Post date:** [March 18, 2013, 10:18pm UTC](https://boards.straightdope.com/t/hardness-of-kidney-stones/653305/1 "2013-03-18T22:18:52Z")
Trivia night question: What’s the hardest substance in the human body? Answer: Tooth enamel. This makes sense to me; tooth enamel is harder than bone, and pretty much everything else in the human body is squishy. However, sick human bodies can produce all kinds of odd substances not normally found in a healthy body. How hard are kidney/gall/salivary stones? Can any of them get as hard as or harder than tooth enamel under any circumstances? ---
**Author:** ![Euryphaessa](https://avatars.discourse-cdn.com/v4/letter/e/c5a1d2/32.png) [@Euryphaessa](https://boards.straightdope.com/u/Euryphaessa)\ **Post date:** [March 18, 2013, 10:47pm UTC](https://boards.straightdope.com/t/hardness-of-kidney-stones/653305/2 "2013-03-18T22:47:58Z")
Gall stones (at least in my sample size of the one that came out of me) are not very hard. You can easily scratch one with a fingernail. ---
**Author:** ![the\_diego](https://avatars.discourse-cdn.com/v4/letter/t/7bcc69/32.png) [@the\_diego](https://boards.straightdope.com/u/the_diego)\ **Post date:** [March 18, 2013, 11:54pm UTC](https://boards.straightdope.com/t/hardness-of-kidney-stones/653305/3 "2013-03-18T23:54:12Z")
The wiki says tooth enamel has a Moh’s hardness of 5 (apatite.) That’s kinda hard, just below feldspar which is a modestly had silicate mineral. Calcic kidney stones precipitate at surface pressure in a process of encrustification around a small “core” so you can imagine that to be soft and crumbly. It’s a lot like travertine wich is calcite that forms in caves (stalactite/stalagmites.) Calcic travertine has a hardness between and 2.5 and 3.5 per wiki. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [March 19, 2013, 8:26am UTC](https://boards.straightdope.com/t/hardness-of-kidney-stones/653305/4 "2013-03-19T08:26:05Z")
Hmm if you’re going into objects not normally found in bodies, how about hip replacements? ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [March 19, 2013, 2:30pm UTC](https://boards.straightdope.com/t/hardness-of-kidney-stones/653305/5 "2013-03-19T14:30:46Z")
Not to hijack, but related - I remember reading that the hardest bone in the human body is the lower jaw bone. Is that true? ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [March 19, 2013, 4:57pm UTC](https://boards.straightdope.com/t/hardness-of-kidney-stones/653305/6 "2013-03-19T16:57:38Z")
> [@echo7tango](#): > > Not to hijack, but related - I remember reading that the hardest bone in the human body is the lower jaw bone. Is that true? No, it cracks all the time. My money is on the petrous portion of the temporal bone. ---
**Author:** ![Reyemile](https://avatars.discourse-cdn.com/v4/letter/r/46a35a/32.png) [@Reyemile](https://boards.straightdope.com/u/Reyemile)\ **Post date:** [March 19, 2013, 5:58pm UTC](https://boards.straightdope.com/t/hardness-of-kidney-stones/653305/7 "2013-03-19T17:58:47Z")
At this point, are we talking about hardness in the technical sense or the colloquial sense? Remember, things that are hard (on the Moh’s scale) can be very brittle. I was referring to the technical meaning, so **the\_diego** ’s response was just what I was looking for.