# Talk:Mohs scale of mineral hardness

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## Linear scale

Question: if the scale isn't linear is there a linear scale that geologists prefer to use? And what exactly is 'absolute hardness'? How is hardness defined (we know what it is intuitively, but what is its physical definition?) Are there SI units for hardness? -- SJK
There is no absolute hardness scale. No units for hardness either. As for what "hardness" really is, I think that is an open question. It would certainly be related to fracture toughness, but that defies analysis as well, relying on laboratory testing and depending on the geometry of the specimen.
A simple search on Google shows there is an 'absolute hardness' scale; in fact, there appear to be at least two: the Rosiwal absolute hardness scale; and the Knoop absolute hardness scale. Also, how can a non-existent scale yield real numbers like the ones in this article (although I've more commonly seen 140000 for Diamond, not the 1500 given above; I suppose this might be the Rosiwal vs. Knoop scales.) -- SJK
What defines hardness depends on the scale you use. The Rosiwal scale measures resistance to abrasion and uses an arbitrary value of 1000 as the hardness of corundum as its basis (diamond comes out to 140,000). The Knoop scale measures how deep a standard diamond pointed tool can cut into a material given a standard amount of pressure pressure (diamond comes out to 7000 in this scale).
Isn't part of the definition of hardness the scratch test (if you can scratch something with something else, that something else is the harder of the two)?
Thats the point of the Mohs scale. Frankly, the most useful materials for hardness testing in the field are fingernails (hardness 2-3) and pocket knives (hardness 5-6). Used in conjunction with luster, crystal habit and color, fingernails and pocket knives do a pretty good job.

The real answer to all this discussion (just above is part of it, too), is that the Mohs scale is a field test, really. All of the things on the scale are minerals - "pure". In the field, one picks up a rock and scratches it. Granite is a great example because it contains quartz, orthoclase feldspar, and a small percentage of a mafic mineral (generally biotite or hornblende) all in one. Even if there were an "absolute hardness", it would be no better, because rocks are not "absolute". There are many variables in rocks, grain structure, grain orientation, inclusions, mixtures - all sorts of stuff. If you have a "Jade Sculpture" and you can scratch it with a knife, it's not jade, it's something else. That's it's use - just one clue as to identifying a rock or mineral. That doesn't make Mohs scale trivial - probably 100% of amateur and pro geologists and minerologists in the world know and use it. Jjdon (talk) 21:35, 2 February 2008 (UTC)

## Absolute hardness of moissanite?

Question: What is the absolute hardness of moissanite? Answer: Moissanite is crystalline silicon carbide, also known as Carborundum, which is on the scale below. The absolute hardness I for one don't know. Jjdon (talk) 20:33, 30 January 2008 (UTC)

## Why is "liquid" listed on the second/extended table?

Question: why is "liquid" listed on the second/extended table? It's been there since the table was created, and I cannot see why it isn't "Talc" there. 194.106.59.2 15:27, 23 Apr 2005 (UTC)

## Nationality of Friedrich Mohs?

MANY SOURCES say that Mohs was Austrian, Many say he was German - The article does not make this clear. I know that he worked and lived mostly in Austria, but this neither makes him Austrian or German by default. His nationality should be clarified.

• Looking at HIS article, it would appear he was Saxon. Which makes him German.

## Absolute hardness?

Maybe someone could link to the appropriate article, or write it if it doesn't exist.--345Kai 09:23, 4 December 2006 (UTC)

I agree - what is the 'Absolute Hardness' scale. Eh?

kind of related: "Moh's Hardness Scale Mnemonic:

Talc Gypsum Calcite Fluorite Apatite Platinum? Quartz Topaz Corundum Diamond

Plagioclase ? (covers a fair range of compositions and hardnesses I know, but mnemonicists don't normally care too much about the details. My DH&Z gives plagioclases as 6-6½.)
A Karley (talk) 05:35, 16 April 2008 (UTC)

It is 2010 now and the 'Absolute Hardness' sticks out as incomplete. It is worse than mentioning a temperature of 620° (Celsius or Fahrenheit your guess). Where Kelvin has something absolute for temperatures, Mohs scale is as much absolute as any other hardness scale. Elegast (talk) 15:01, 24 June 2010 (UTC)

## Window glass

I think window glass is somewhere near quartz, since the two are very similar in composition. Thus I have changed it to 6.5 unsigned

Very scientific.68.145.207.92 03:03, 11 January 2007 (UTC)
Must be right. I think graphite and diamond must be pretty similar as well. I mean, it's basically the same thing. Dept of Alchemy 21:08, 20 February 2007 (UTC)

Window glass's main component is silicon since it's made from sand. The snare (talk) 02:11, 17 March 2016 (UTC)

## Mohs Scale

Diamond is 10 on Mohs scale. For some reason diamond showed up as 15 on the table, so I changed that. Dept of Alchemy 21:10, 20 February 2007 (UTC)

He must have confused it with the Ridgeway scale, which modified by Moh's by putting diamond at 15 J1812 (talk) 11:52, 17 December 2014 (UTC)

with the mohs scale table, can we add carbonado about it has the same strength as diamond and is a fairly notable example of a mohs 10 that few people have heard of. : D please add. Tincanmansiimon (talk) 19:09, 12 September 2012 (UTC)

I removed the paranthetical diamonds exception from "All readily available (except diamonds)" Diamonds are certainly readily available--you can get them at hardware stores all over the world! And they are by no means a rare mineral. (the reasons why they are so high-priced isn't because they are rare.) As a matter of fact, if you were challenged to find flourite or diamond in a limited amount of time, for prize money, unless you happen to live near a university with a geology department you'd probably be better off choosing to search for a diamond. Brentt 22:33, 23 February 2007 (UTC)

I take your point, but fluorite isn't exactly hard to find either. It's moderately popular in jewellery. Look for "Blue John". A Karley (talk) 05:24, 16 April 2008 (UTC)

## Natural occurring materials harder than diamond affecting Mohr's Scale

Newly occurring materials harder than diamonds have been recently discovered. It is unclear how this will affect Mohr's scale. At the very least some wording will need to be changed on this page to incorporate this; ie: "As the hardest known naturally occurring substance, diamond is at the top of the scale." I am not sure how mentioning the new materials should be handled and I can't find anything on how it might affect Mohr's scale (I would guess the materials would be assigned a number above 10 rather than renormalization).

User:Nicf 08:26, 18 February 2009 (UTC) —Preceding unsigned comment added by 69.181.124.22 (talk)

For further reading, you may also find the following page of use: http://www.itvnews.tv/Sci-Tech/Science/diamond-is-no-longer-natures-hardest-material.html

79.71.190.207 (talk) 00:12, 20 February 2009 (UTC)

## Hardness of boron

Delete reference to the article of Zarechnaya et al. These people were not the first ones to measure the hardness of boron. Weintraub was the first one to give qualitative (9.5 by Mohs scale) measurement, Solozhenko et al. were the first to give quantitative measure (50 GPa).

I see that user Materialscientist has persistently reverted deletion of the the reference to Zarechnaya et al. I also see that on WP this user has generally created a lot of references to these people (group of N.Dubrovinskaia). I am aware that Materialscientist is a collaborator of N.Dubrovinskaia, and this should make him ineligible to promote her worksNo more D (talk) 19:42, 11 September 2010 (UTC)

None of the instances talks about priority, thus your concerns do not apply, but your personal attacks are not appreciated. Materialscientist (talk) 23:28, 11 September 2010 (UTC)

If you agree that Zarechnaya et al. (2009) do not have priority over Weintraub (1911) and Solozhenko (2008), then I see no point in adding their reference. The journal where Dubrovinskaia's group (Zarechnaya et al.) published their work is not freely available, but actually quite expensive. These people were not the first and obtained results identical to previous works. What are the reasons to include their paper? Will you equally insist on adding the 5th, 25th, 101st determinations of boron's hardness? As to personal attacks - there are none. It is well known on WP that you, Materialscientist, are Dubrovinskaia's collaborator. This has been said many times in WP and you never denied that you are Dubrovinskaia's collaborator. This explains why you so eagerly put her name in so many articles. But WP should not suffer from this. Please do not reinstate this paper again, and refrain from adding Dubrovinskaia in this or other WP articles without truly good reasons, or I will have to complain about this. No more D (talk) 04:45, 17 September 2010 (UTC)

The reference to Zarechnaya's paper really does not belong here. It is not the first or even the second paper on the topic, but third! Moreover, the paper is scientifically incorrect, see http://arxiv.org/abs/0908.2126 and http://arxiv.org/abs/1005.4821. The persistent addition of this reference by Materialscientist only confirms the above made suggestion that he has a personal involvement with that paper or its authors. — Preceding unsigned comment added by 79.164.109.129 (talk) 10:35, 9 July 2011 (UTC)

TO MATERIALSCIENTIST: Please stop adding irrelevant and scientifically incorrect reference to Zarechnaya. Please stop adding references to works of your friends, especially those references that were proven to be scientifically incorrect. Those references are not legitimate and if they are included, for objectivity they must be accompanied by their critique which their authors have not addressed. If Materialscientist wants to justify the addition of this reference, would he please run it through the Talk-pages first. Thank you! — Preceding unsigned comment added by 79.164.109.129 (talk) 10:48, 10 July 2011 (UTC)

That someone is someone's friend, and that something was proven incorrect are mere speculations. Your are banned user Aoganov, who came to wikipedia with a single purpose to promote your work, and discredit anyone who stands on your way, by any means possible. I got involved in this whole issue only because someone from Dubrovinskaia group contacted me on my talk. I was first skeptic to all parties for quite some time, and then you showed what you're up to. Cease and desist. Those references (yours and of Dubrovinskaia) stand here because of WP:NPOV, to present both sides of research. Materialscientist (talk) 11:23, 10 July 2011 (UTC)

## Inconsistencies

Under the table, the text says that a steel file has a hardness of 6.5 and a streak plate has a hardness of 7. Neither of the two footnoted links in that section give a hardness for a "steel file". One gives a "steel nail" as 5.5, and the other gives a "steel needle" as 6.5. They give different hardnesses for a streak plate, 6.5 vs. 7. The subsequent intermediate hardness table lists steel as 4 to 4.5, and hardened steel as 7.5 to 8.NoJoy (talk) 17:34, 12 October 2010 (UTC)

## WP:OR removed

I have removed a statement

Since the invention of the Mohs scale of mineral hardness, there have been reports of materials harder than the highest mineral on the scale, diamond; so the Mohs scale may be changed in the future.[1]

Per WP:OR - neither it is present in the cited reference nor there is any reliable experimental report of material harder than diamond. Materialscientist (talk) 01:07, 15 March 2011 (UTC)

Look at the links in the comments above. You are wrong. — Preceding unsigned comment added by 175.180.196.236 (talk) 09:49, 7 June 2011 (UTC)
There are two types of reports on materials "harder than diamond". One is experimental work on ADNR, which is diamond, but in a nanocrystalline form. Another is theoretical, on lonsdaleite - needs to be confirmed by experiment, which showed that lonsdaleite produced so far is too defective and has a hardness significantly lower than diamond. Materialscientist (talk) 10:06, 7 June 2011 (UTC)

References

1. ^ Irifune, Tetsuo; Kurio, Ayako; Sakamoto, Shizue; Inoue, Toru; Sumiya, Hitoshi (2003). "Materials: Ultrahard polycrystalline diamond from graphite". Nature. 421 (6923): 599–600. doi:10.1038/421599b. PMID 12571587.

## Hardness of chromium

On the same wikipedia page, elemental chromium is stated as having a hardness of 8.5 on Moh's scale and then in the last chart it is written 9. Chromium is absolutely NOT as hard as corundum, since Moh's scale is not a proportional scale, and with around 1GPa Vickers hardness, chromium doesn't compare well with alumina, in other words, there is a substantial difference between 8.5 and 9 in Moh's scale. Mindat.org is NOT a reliable source, there are loads of inconsistencies and inaccuracies on that site, why is it referred to so often on wikipedia? — Preceding unsigned comment added by 82.240.163.245 (talk) 22:54, 5 February 2012 (UTC)

Thanks, I have lowered 9 to 8.5. There is an intrinsic problem with metals that their hardness can vary several times or more depending on the history (thermal and mechanical) of preprocessing. Materialscientist (talk) 02:01, 6 February 2012 (UTC)

I'd very much like to know the hardness range of pure chromium for various states of annealing, as unfortunately I don't have access to hardness- testing equipment. However, from my own experiments, for coarsely crystalline, slowly cooled- from- melt cast metal of both 99.15 and 99.9% purity, quartz and high carbon steel will scratch it. Anyone else have reason to suspect that even 8.5 mohs hardness is too high? — Preceding unsigned comment added by Elementperson (talkcontribs) 19:43, 12 April 2013 (UTC)

## Mnemonic

There is a mnemonic for remembering the Mohs scale. Can't remember it (oh, the irony..). Shouldn't that have a mention? VenomousConcept (talk) 13:47, 2 March 2012 (UTC)

Looked it up, the mnemonic is : Toronto Girls Can Flirt And Other Queer Things Can Do VenomousConcept (talk) 14:56, 2 March 2012 (UTC)

## Carbide

Error! stishovite is harder than tantalum carbide(<9.5), invert them in table! — Preceding unsigned comment added by 84.221.100.6 (talk) 13:57, 12 May 2012 (UTC)

References please --Chris.urs-o (talk) 14:23, 12 May 2012 (UTC)

Gross mistake: like other metal carbides, hardness of tantalum carbide is clearly <9.5, while stishovite has vickers of ~30GPa (~9.5 Mohs). — Preceding unsigned comment added by 78.12.115.168 (talk) 21:54, 12 May 2012 (UTC)

I updated the stishovite and this article. Mohs scale is very approximate, and there is much spread in stishovite hardness (anisotropy, sample dependence - stishovite samples are relatively rare), thus it is often uncertain which material is harder. Materialscientist (talk) 10:09, 13 May 2012 (UTC)

Much more lower tantalum carbide at 9-9,5. — Preceding unsigned comment added by 84.220.110.78 (talk) 13:58, 13 May 2012 (UTC)

## Edit request on 15 May 2012

Tantalum carbide must change position in table.

84.221.101.98 (talk) 11:53, 15 May 2012 (UTC)

Why? Dru of Id (talk) 12:40, 15 May 2012 (UTC)
Tantalum carbide is close to Cr in Vickers hardness, and thus should be something like 8.5, which is what I have changed in the article just now. Materialscientist (talk) 12:50, 15 May 2012 (UTC)
► But it's better at 9-9.5.
Unreliable page. Also, look at Vickers hardness, not Mohs. Mohs scale is very non-linear around 9 - compare actual hardness values of metals (Cr) and oxides. Materialscientist (talk) 03:16, 16 May 2012 (UTC)
-->OK, consistent with http://en.wikipedia.org/wiki/Tantalum_carbide. — Preceding unsigned comment added by 84.221.86.200 (talk) 01:28, 20 May 2012 (UTC)

## Edit request on 24 May 2012

Titanium diboride and stishovite are at wrong position in table: with their ~30 GPa Vickers they should be lowered to 9-9.5, not 9.5-10 (at least ~40Gpa) wherein B6O and ReB2 could be placed. 78.12.118.38 (talk) 22:01, 24 May 2012 (UTC)

Values vary from report to report, and 30 or 40 is quite the same for the Mohs scale. Some reshuffling might be needed, but better one. Materialscientist (talk) 22:31, 24 May 2012 (UTC)

## How are intermediate values determined?

Early on, it explains that Mohs scale is an ordinal scale. In the table that follows, we see that the absolute hardness values are irregular with respect to the Mohs values. This seems to be saying that only the integer values from 1 to 10 inclusive are defined, and no substance can be said to have a particular Mohs value outside this set – it can just be said to be "between 5 and 6" or "below 1", for instance.

And yet immediately below the table, and in the section that follows, specific non-integer values are given for a number of materials. Does this mean that Mohs added these intermediate points to the scale since originally publishing it? Or that somebody has invented a formula (maybe a piecewise linear, or piecewise exponential, or cubic spline, or just a 9th degree polynomial) whereby the sclerometer output for a given material can be converted into a Mohs value? If the article is going to mention specific intermediate values at all, it should at least explain them. — Smjg (talk) 18:37, 16 February 2014 (UTC)

## Doesn't mean a lower hardness scale material can't effect a higher one

Maybe there should be a note of this. For example, a steel axe is much harder than any wood, but this doesn't mean that your steel axe will never wear out chopping trees/wood. Nor does it mean if have a tongue ring that you can't scratch the enamel off your teeth with it with repeated rubbing. There's more to it than hardness, what about the amount of force used. A spinning steel blade circular saw could cut a tooth couldn't it- even if the tooth is a higher hardness. The snare (talk) 02:10, 17 March 2016 (UTC)

## Semi-protected edit request on 28 January 2016

208.108.212.76 (talk) 13:21, 28 January 2016 (UTC) Mohs scale is a scale for minerals and their hardness, doing test like the scrach test, and hardness test.

Not done - that is what the article states - Arjayay (talk) 14:51, 28 January 2016 (UTC)

## The Mohs Scale

Is there a reason why the article does not use the definite article, or is that an omission? I.e., is there a reason to say "Mohs scale of mineral hardness is…" instead of "The Mohs scale of mineral hardness is…" ? –Jérôme (talk) 11:23, 13 November 2016 (UTC)

@Jérôme: You're talking about the lead sentence? I agree, it sounds awkward. The rest of the article uses "the" in front of "Mohs". I'll go fix that sentence. — Gorthian (talk) 00:10, 14 November 2016 (UTC)

Now that there are expectations that Lonsdaleite manufactured/fabricated in a lab will be harder than diamond, when will we be able to add it to the scale/list/table? 77.126.20.27 (talk) 23:30, 13 December 2016 (UTC)

## Specifying some formulae as 'OH-' and others as just 'OH'

In the table giving the chemical formulae of the minerals making up the scale, for talc we have "(OH)2", but for apatite "(OH-,Cl-,F-)", and topaz "(OH-,F-)2". In the Wikipedia entries for apatite and topaz, the article doesn't give the "-" indicating the ionic charge, as we don't for talc in this article. Is there any reason for the inconsistency? Peace Makes Plenty (talk) 16:28, 23 February 2017 (UTC)

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