Learning Center What is a mineral?The most common minerals on earth Information for Educators Mindat Articles The Elements The Rock H. Currier Digital Library Geologic Time

Minerals by Properties Minerals by Chemistry Advanced Locality Search Random Mineral Random Locality Search by minID Localities Near Me Search Articles Search Glossary More Search Options

The Mindat Manual Add a New Photo Rate Photos Locality Edit Report Coordinate Completion Report Add Glossary Item

Mining Companies Statistics Users Mineral Museums Clubs & Organizations Mineral Shows & Events The Mindat Directory Device Settings The Mineral Quiz

Photo Search Photo Galleries Search by Color New Photos Today New Photos Yesterday Members' Photo Galleries Past Photo of the Day Gallery Photography

Discussions

💬 Home 🔎 Search 📅 Latest

╳Discussions

💬 Home 🔎 Search 📅 Latest

Groups

Recent Images in Discussions

GeneralIs this true???

17th Sep 2012 22:03 UTCRick Dalrymple Expert

I have never heard of diamonds that are twice as hard as regular diamonds, but I am not a diamond guy. This sounds more like a con that true. Can any experts shed some light on this for me?

http://news.yahoo.com/russia-reveals-shiny-state-secret-awash-diamonds-131212873.html

17th Sep 2012 22:14 UTCFred E. Davis

Hmm... Seems to me the story shares some similarity to the film "Spinal Tap." In this case, their diamonds go past 10, all the way to 11. ;-)

17th Sep 2012 22:25 UTCRon Layton

I just read the article and reached the same conclusion. Well, there go's the good old Mohs scale. I guess the asteroid impact made them "super" diamonds.;-) What next.

17th Sep 2012 22:32 UTCRick Dalrymple Expert

I am glad it wasn't just me scratching my head:-S

17th Sep 2012 23:36 UTCClosed Account 🌟

An Austrian writer and philosopher once said that „journalists are people that by definition are absolutely clueless about the matters they write about“. This seems to hold true for the quoted article on yahoo.

Having said that, the question raised in this thread – “Is it true?” – is answered.

Some questions that could be asked in this matter are:

By what scale?

In which direction?

Which modification of carbon?

If you look at the different modifications of carbon, you will find that graphite for example is actually harder in one direction than diamond in a certain direction. This comes from the anisotropy of the hardness in both.

Now if somebody finds a modification of carbon that is “twice as hard” as diamond, then it is no longer a diamond as the hardness of diamond is related to its crystal structure and the forces that hold this structure together. This is basically the same in all diamonds worldwide (if you disregard the effects of trace elements).

Branko

18th Sep 2012 00:19 UTCKeith Wood

I have read that ballas diamonds are harder than typical diamonds. They have a naturally round form (google them) that presents a face with a harder surface, and since they are round, that is the only face presented. John Betts provides this information.

So yes, this is possible. I would like to see even better support for this information, however.

18th Sep 2012 00:27 UTCKeith Wood

The hardness described may also be related to the radial structure's resistance to cleaving, which is a contributor to measured hardness. In this sense, the Mohs hardness might be the same as any diamond, but the resistance to cleaving might make them tougher in an industrial application, just like it is easier to smash a quartz crystal with a hammer than it is to smash a similarly shaped piece of very competent quartzite.

18th Sep 2012 00:55 UTCDavid Von Bargen Manager

Well, this scoop is only about 10 years out of date

http://www.sciencedirect.com/science/article/pii/S1631071303001317

http://www.sciencedirect.com/science/article/pii/S0012821X09007389

I don't think that DeBeers has anything to worry about. (you need a SEM to see these things).

18th Sep 2012 01:09 UTCOwen Lewis

It seems to me that to discuss the hardness of Diamond in terms of Mohs's scale defies logic - but so do some other attempts to relate minerals to that very basic and irrational scale :-(

Diamond (Mohs 10) is shown to be 5 to 6 times as hard as Corundum. (Mohs 9). Diamond IIa has been shown to have an absolute hardness that varies acording to the direction of the test from 137 to 167 GPa. By the same test method (nanoscale scratch testing using a Fullerite stylus of prescribed dimensions). Corundum shows a hardness of 23 GPa. In other words the variance in hardness demonstrated in a single Diamond crystal is greater than the difference in hardness between Corundum and Talc. This work was done in the USSR at the end of the '80's and published in Western scientific literature in the early 90's. I.e. this information is scarcely news any more.

18th Sep 2012 01:39 UTCAnonymous User

I just read this article and was wondering the same thing RE: hardness. Keep in mind that hardness in diamond is also related to the internal growth structure - i.e. single-stage growth results in a harder diamond than multi-stage. I've read that this is the reason that many Australian diamonds are harder than most other diamonds.

Diamonds are very complex, and hardness (as well as other properties) can and does vary according to many variables. While the reporters may be as clueless as usual, there may be some truth to "extra hardness."

18th Sep 2012 03:34 UTCRick Dalrymple Expert

Thanks, I appreciate everyone's input. I have never considered diamonds could be different hardness's even thought I know many other minerals exhibit this property.

I didn't understand the size of the diamonds at this location either. If you need an SEM to see these diamonds how to they test the hardness?

18th Sep 2012 04:16 UTCDavid Garske

My first Ph.D. thesis at the University of Michigan was studying directional hardness in diamonds. The hardest and softest directions are both on the cube face at 45 degrees to each other, one tilting the stone a little bit away from parallel. Critical to a diamond cutter, the hard direction will cut through a grinding wheel, soft direction is very cuttable. (When you put the stone on the wheel, you can hear the hardness difference.) Also if you are mounting diamonds in a cutting tool, such as a diamond bit, the bit will cut faster and last longer if the stones are properly oriented. Work was done in the early 1960's.

Dave

18th Sep 2012 05:07 UTCDean Allum Expert

During the 1990's I heard of attempts of increasing the hardness of cutting tools by exposing them to ion-implantation which made their surface amorphous. The theory was that this would help prevent cleaving at the microscopic level. Since ion implantation is expensive, it is cheaper to just replenish the worn tools.

Perhaps there is another principle involved with these diamonds. If they were formed AND shattered by a significant blast, then maybe all the 'brittle' portions are obliterated, with just HARD splinters remain (survival of the hardest).

-Dean Allum

18th Sep 2012 05:44 UTCJenna Mast

If this is true it's rather exciting news...I managed to wear down my diamond tipped dremel bit on an albite matrix.

20th Sep 2012 18:52 UTCRay Hill Expert

If you talk with diamond cutters, they will tell you that some diamonds, like those from Guyana, are much harder than others. This may be directional, but it also may be "toughness" like the difference between quartz and agate. I am not sure.

21st Sep 2012 01:52 UTCOwen Lewis

David Garske Wrote:

-------------------------------------------------------

> My first Ph.D. thesis at the University of

> Michigan was studying directional hardness in

> diamonds. The hardest and softest directions are

> both on the cube face at 45 degrees to each other,

> one tilting the stone a little bit away from

> parallel. Critical to a diamond cutter, the hard

> direction will cut through a grinding wheel, soft

> direction is very cuttable. (When you put the

> stone on the wheel, you can hear the hardness

> difference.) Also if you are mounting diamonds in

> a cutting tool, such as a diamond bit, the bit

> will cut faster and last longer if the stones are

> properly oriented. Work was done in the early

> 1960's.

> Dave

Observation of the phenomenon and coming to grips with its effects are much older - as I'm sure you know, Dave.

The first Diamonds to be worn as jewels were natural crystal forms (from about 300BC, in India). Octahedrons 'improved' by cleavage began to appear from 1300(Venice). *Most* transparent Diamonds will cleave relatively easily. To produce a jewel with a flat table from an octahedral crystal requires that one of the pyramidal points be sawn off parallel to the square central girdle. Diamond will not cleave in that plane but can be sawn relatively easily (compared to cutting in other directions). This technique became known c.1450. Because of the limits on the sawing techniques and lack of a full understanding of stone's refractive and reflective properties, further cuts were added to the jewel design only slowly over the next 300 years, Diamond jewels remaining relatively dark stones with few cuts additional to the octahedral cleaving and central table (with the single exception of the Rose cut). During this time, these jewels show relatively little brilliance, compared to modern cuts, but show good fire. The 19th Century brought improved saws that permitted gem quality stones to be cut more or less as required and as a mathematical understanding of the handling of light in Diamond suggested that the best effects could be obtained. The precursors for the modern Brilliant cuts, the Old Mine and Old European cuts, appearing in the 1800's, were a marked step forward. With many still in circulation today, these can easily be identified by the smallness of their tables relative to the diameter of the stones - a historic legacy. They also still do not show the full brilliance that was only to be made possible later, with the advent of better perfected designs and cutting techniques in the 20th Century.

The question of Diamond harder than Diamonds AIUI relates mainly to some translucent/opaque some Diamonds of industrial grade.in which, sho'nuff, resistance to sawing can be extreme because the parting planes on which the cutter (used to have to) rely do not appear to exist.

21st Sep 2012 04:25 UTCD Mike Reinke

Great thread, though the 'news' article was pathetic.

"When a meteor plows into a diamond field' Yeah, that happens regularly.

Science aside, who are 'they'? And who revealed that nugget of truth to the reporter?

Let alone keeping a vast diamond field secret for 40 years. Mums da woid. These are communist politicians. ( not that others are better..)

Like David said, DeBeers isn't worried.

Fred totally nailed it with the spinal tap reference, thank-you, Fred!

22nd Sep 2012 20:58 UTCJohn Betts

The octahedral faces of a diamond was recently tested and approximated to be 500 times harder than the cubic face -- though testing this was extremely difficult due to the absolute hardness. This is why diamond cutters must orient the "grain" of the crystal when cutting the facets (if you cross the grain it will never take a polish).

True "Ballas" diamonds are polycrystalline, with radiating internal structure that presents only octahedral faces on the surfaces. Ballas diamonds are set in the bits of rock drills for this reason. When the diamond cleaves during drilling it presents another octahedral face.

Monocrystalline spherical diamonds are not true Ballas and are recognized by microscopic parallel cubic faces.

An early reference is:

http://www.minsocam.org/msa/collectors_corner/arc/diamond_hardness.htm

If I locate the recent study I will add the reference later.

22nd Sep 2012 21:20 UTCJohn Betts

Here is an image of a Ballas diamond that broke through the middle. Though the diamond is crude you can make out the radiating/layered internal structure.

22nd Sep 2012 22:13 UTCOwen Lewis

John,

Your comment of 'difficulties in testing due to absolute hardness of Diamond' is well taken. This was a real problem until the discovery of Fullerite (C60). After that it was only a matter of time before accurate measurements of the varying hardness of Diamond became practical. These were, I believe. first carried out in a state science institute in the USSR in late '80's.

The secret to accurate testing is that the piece under test shall have a planar surface and:

- The stylus for the scratch test be fashioned in Fullerite or some other substance substantially harder than the specimen under test (Diamond in this case).

- The stylus have a prescribed and documented profile.

- The stylus be applied to the test piece normal to its surface plane.

- The force applied to stylus be accurately metered (these days in SI, i.e Pascals or, in this case, GigaPascals.

- A settled definition of what that measurement of force represents. It is the force that when applied to the stylus is just sufficient for the tip of the stylus to cause a permanent deformation of the surface of the test material. This is the measure of scratch resistance (= hardness).

Different types of Diamond demonstrate different hardnesses when measured accurately.The Soviet work (since emulated elsewhere) recorded that ,for Diamond type IIa a hardness of 137 GPa was measured on the 100 plane and 167 GPa was measured on the 111 plane. By way of comparison, C60 has a hardness of around 310 GPa. If you are interested, I can let you see a .XPS of a short paper on this work translated and published in English by Elsevier on 1998 (Ultrahard and superhard phases of Fullerite C 60 : comparison with diamond on hardness and wear). Or, with others, you can purchase through Elsevier or visit your local Uni library.

Relevant to this thread is speculation as to whether 'Balas Diamond' 'Carbonado Diamond' etc. exhibit features of crystalline structure which approach the structure of C60. Anyone have hard data on this?

23rd Sep 2012 01:30 UTCBart Cannon

This is truly an interesting and informative thread and should be re-named "Variable Hardness of Diamonds" rather than "Is this true ?".

I have learned a great deal from this thread. I was not very tempted to open the thread, but did so on a lark. I was rewarded for my lark.

Back during the "diamond rush" started by nearly penniless SEM operator Chuck Fipke, I did quite a bit of diamond indicator mineral work until one of the major exploration mining companies installed four electron probes in Kelowna, B.C. Fipke's only problem these days is figuring out how to deplete his bank account before he dies.

There is a modern book describing the Fipke revelations and diamond exploration in the far North of Canada.

"Barren Lands" by Kevin Krajick.

Probably illustrating the best example of a commercial application of the use of the electron microprobe and mineral exploration.

Bart

23rd Sep 2012 03:28 UTCLinda Smith

Bart, that is one book that is in my library. Great read. why is it that I am not surprised to hear of your connection to Fipke!

23rd Sep 2012 04:40 UTCRick Dalrymple Expert

Thanks everyone for this great information. I have never really considered diamonds to be of much interest. I feel like I have had an epiphany about diamonds. I look forward to more postings and information.

27th Nov 2013 23:55 UTCJohn Betts

I stand corrected.

The 500x value came from a study comparing grinding resistance.

One article listed 100x difference in hardness: http://www.minsocam.org/ammin/AM38/AM38_108.pdf

But the latest citation focusing not on grinding but on scratching using superhard fullerite yields a 20% difference in hardness. See: http://nanoscan.info/wp-content/publications/article_02.pdf

28th Nov 2013 19:42 UTCPeter Piper

I have plenty of broken diamonds :-)

30th Nov 2013 22:43 UTCJohn Betts

This is a summary of the hardness difference in diamond faces.

Determining diamond hardness has always been problematic. Standard indentation tests like the Knoop, Rockwell, Vickers, Shore and Brinell failed because no indenter material had sufficient hardness to make an impression on a diamond crystal. The cubic face of a diamond is harder than all other known materials. But the octahedral face of diamond was known to be even harder. Because indentation tests were insufficient in determining the relative hardness of the diamond faces, researchers relied on comparing grinding resistance to determine relative hardness.

Grinding/polishing a diamond using diamond abrasives indicated large differences in hardness between the cubic and octahedral faces with variations depending on grinding direction/orientation (what diamond cutters call cutting against the grain or with the grain).

Denning reported measurable grinding hardness differences in excess of 500 times harder than the softest orientation of the cubic face using grinding the methodology. His upper limits of hardness were interpolated because the hardest face-orientations failed to show satisfactory results during grinding (see figures 3 and 4 in American Mineralogist, 1953, vol. 38, page 108-117).

However, the discovery of ultrahard fullerite (C₆₀) provided a material that was harder than the hardest face of a diamond. Fullerite has a hardness of 310 gigapascals (GPa) on the Vickers Scale. Indentation tests using a fullerite indenter finally were able to yield hardness results for diamond cubic face of 137 ± 6 GPa and on the octahedral face of 167 ± 5 GPa, a difference of approximately 20% (Journal of Materials Research, 1997, vol. 12, pages 3109-3114)

This small difference in relative hardness makes a large difference when polishing diamonds. Diamond abrasives easily polishes cubic faces in the correct grinding direction, but slowly polishes octahedral even in the best grinding direction and no polish is possible in certain grinding direction. Until ultrahard fullerite abrasive becomes available, the 20% hardness difference between the faces will still result in large differences in polishing time.

1st Dec 2013 14:03 UTCRock Currier Expert

I think this should be in a mindat article.

1st Dec 2013 14:45 UTCSpencer Ivan Mather

No it is not true, but diamonds like some other minerals have different harnesses when cut from different angles, and one of those crystalographic orientated angles has a hardness of 1,000 times more that the rest of the diamond, this is one of the reasons for the difficulty in the cutting and polishing of diamonds..

Spencer

1st Dec 2013 19:57 UTCElise Skalwold

John Betts Wrote:

-------------------------------------------------------

> Determining diamond hardness has always been

> problematic.

That is for sure. When I was researching the nano-polycrystalline diamond (NPD) in order to write something that would hopefully interest the gemology community, I had to sift through some very "dense" papers about hardness properties of diamond - and then try to condense them into something readable to provide background on the specimens I was studying. It was an education into how complicated the topic of this thread gets. Two of interest here might be:

"Carbon polymorphism in shocked meteorites: Evidence for new natural

ultrahard phases" Tristan Ferroir, Leonid Dubrovinsky, Ahmed El Goresy, Alexandre Simionovici,

Tomoki Nakamura, Philippe Gillet Earth and Planetary Science Letters 290 (2010) 150–154

"Natural and synthetic polycrystalline diamond, with emphasis on ballas" Lux B., Haubner R., Holzer H., DeVries R.C. International

Journal of Refractory Metals and Hard Materials, (1997) Vol. 15, No. 5–6, pp. 263–288

For background on NPD, see the the reference list at the end of this overview paper: Skalwold, E.A. (2012) Nano-polycrystalline diamond sphere: a gemologist's perspective. Gems & Gemology, Vol. 48, No. 2, pp. 128-131. http://www.gia.edu/doi/10_5741-GEMS_48_2_128

and follow-up paper, Skalwold, E.A., Renfro N., Shigley J.E., and Breeding, C.M. (2012) Characterization of a synthetic nano-polycrystalline diamond gemstone. Gems & Gemology, Vol. 48, No. 3, pp. 188-192 http://www.gia.edu/doi/10_5741-GEMS_48_3_188

Best wishes,

Elise

Mindat.org is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization.
Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: April 23, 2024 20:23:15

Go to top of page