<p>This looks like something unquestionably from a minerology textbook, the content of which I was never great at learning (or testing in). Regardless, here's my take on your info and question.</p>
<p>First, make sure you understand 2 terms enough before proceeding: 1] indices (for a mineral) and 2] elastic constants (@f.thorpe's comment motivates this).</p>
<p>Now that you have said terms defined in this context and know (approximately) what they mean, let's proceed with a simple, short take for an answer...</p>
<p>When rocks (or more specifically minerals) are &quot;deformed (i.e. &quot;strained&quot;) in labs, in earth, or seismic energy, they &quot;compress&quot; and/or &quot;extended&quot; in different ways (and directions). Now, here's where I carefully throw out an important and hard-to-pronounce-at-first term: <strong>mechanical anisotropy</strong>. As a short answer, this is likely what's going on. However, for more info, read on...</p>
<p>Anisotropy is basically everywhere. Optics, seismics, ...mechanics - you name it! For this example, though, it's the non-linear relationship between &quot;stress&quot; (i.e. &quot;load&quot;) and &quot;strain&quot; (again, a <em>ratio of deformation</em> - keep in mind that it's unitless). Think of it this way: when I push the keys on my keyboard to try and provide an answer here, they are (at a very small scale) mechanically shortened vertically and extended laterally. However, if I did the same action with typing and instead the key compressed laterally (<em>whoa</em>, don't believe me - <a href="https://www.sciencedirect.com/science/article/abs/pii/S0261306915002812" rel="nofollow noreferrer">here's a common material</a> that does this), that could be quantified as negative elastic constant (note though that &quot;elastic constant(s) is a general term includes a lot of more specific terms provided <a href="https://se.copernicus.org/articles/11/259/2020/" rel="nofollow noreferrer">here</a>).</p>
<p>If you examine that last link (even just the intro), I think that'll help guide more understanding here.</p>

CC BY-SA 4.0
2023-10-25T03:07:05.543Z
so what do you mean ? What could be the possible hypothesis that it has negative value in particular direction only?
mark22
CC BY-SA 4.0
2023-10-26T15:19:22.720Z
I'll add more and respond to the first question once we have a reference to the image above. So, please supply that. As for your second question, can you please rephrase it? I don't understand it with its current wording.
nate
CC BY-SA 4.0
2023-10-23T14:04:36.887Z
2023-10-23T14:04:36.887Z
nate
<p>In this table of elastic constants, indices m = 1 and n = 4 result in negative values.  What could the reason be?</p>
<p><a href="https://i.sstatic.net/Tv4Os.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Tv4Os.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2023-10-21T15:01:30.730Z
best to give a source for the table please :)
JeopardyTempest
CC BY-SA 4.0
2023-10-21T21:39:42.627Z
Not a geologist, so I had to look up what these constants meant.  It could mean that in that specific translational direction, deformation would not occur in the direction of force, perhaps something specific to lattice structures.  Hopefully a geologist can chime in.  Putting these here for reference: https://www.nature.com/articles/sdata20159 https://www.usgs.gov/publications/elastic-constants-calcite-0 https://www.sciencedirect.com/topics/materials-science/elastic-constant
f.thorpe
<geology><geophysics><geochemistry>
What is the reason that some elastic constants are negative?
mark22
# What is the reason that some elastic constants are negative?

(Asked by: username_0 on 2023-10-21)

In this table of elastic constants, indices m = 1 and n = 4 result in negative values. What could the reason be?

[![enter image description here](https://i.sstatic.net/Tv4Os.png)](https://i.sstatic.net/Tv4Os.png)

**Tags:** geology, geophysics, geochemistry

> **Comments:**
> **username_1**: best to give a source for the table please :)  
> **username_2**: Not a geologist, so I had to look up what these constants meant.  It could mean that in that specific translational direction, deformation would not occur in the direction of force, perhaps something specific to lattice structures.  Hopefully a geologist can chime in.  Putting these here for reference: https://www.nature.com/articles/sdata20159 https://www.usgs.gov/publications/elastic-constants-calcite-0 https://www.sciencedirect.com/topics/materials-science/elastic-constant  

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## 1 answers

### Answer by username_3 on 2023-10-23. Score: 1 | Accepted answer

This looks like something unquestionably from a minerology textbook, the content of which I was never great at learning (or testing in). Regardless, here's my take on your info and question.

First, make sure you understand 2 terms enough before proceeding: 1] indices (for a mineral) and 2] elastic constants (@username_2's comment motivates this).

Now that you have said terms defined in this context and know (approximately) what they mean, let's proceed with a simple, short take for an answer...

When rocks (or more specifically minerals) are "deformed (i.e. "strained") in labs, in earth, or seismic energy, they "compress" and/or "extended" in different ways (and directions). Now, here's where I carefully throw out an important and hard-to-pronounce-at-first term: **mechanical anisotropy**. As a short answer, this is likely what's going on. However, for more info, read on...

Anisotropy is basically everywhere. Optics, seismics, ...mechanics - you name it! For this example, though, it's the non-linear relationship between "stress" (i.e. "load") and "strain" (again, a *ratio of deformation* - keep in mind that it's unitless). Think of it this way: when I push the keys on my keyboard to try and provide an answer here, they are (at a very small scale) mechanically shortened vertically and extended laterally. However, if I did the same action with typing and instead the key compressed laterally (*whoa*, don't believe me - [here's a common material](https://www.sciencedirect.com/science/article/abs/pii/S0261306915002812) that does this), that could be quantified as negative elastic constant (note though that "elastic constant(s) is a general term includes a lot of more specific terms provided [here](https://se.copernicus.org/articles/11/259/2020/)).

If you examine that last link (even just the intro), I think that'll help guide more understanding here.

> **Comments:**
> **username_0**: so what do you mean ? What could be the possible hypothesis that it has negative value in particular direction only?  
> **username_3**: I'll add more and respond to the first question once we have a reference to the image above. So, please supply that. As for your second question, can you please rephrase it? I don't understand it with its current wording.  

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