FMF - Friends of Minerals Forum, discussion and message board

[Jim]

How large of cubic diamonds have you seen in fine quality -- defined as nice luster, equant, no damage and reasonable translucence?

Thanks!

[John S. White]

I suggest that you go to this page of the web site of John Betts

https://www.johnbetts-fineminerals.com/jhbnyc/diamdiag.htm

[Jim]

Thx, John

Yes, I have known John Betts and his site for years now. But what I have had a difficult time finding info about is the size of fine diamond cubic crystals on the specimen market. Most nice ones I have seen offered are one carat or less. Have you seen them get much larger while retaining symmetry, fine luster and over all fine quality?

[Pete Modreski]

Hi Jim,

I think your question is a good one that probably does not have any easy-to-find answer, likely because no one (?) has thought to ask or search for the answer to this particular question.

For example, the book, Diamonds, by Eric Brunton (2nd ed., 1978) says about cubic diamonds (p. 367),

"Cubic crystals are relatively uncommon, but are almost entirely confined to low quality (industrial) stones."

I think to get a real answer to this, you'll need to talk to some one or other who is really one of the world's gem experts on diamond crystals; perhaps one of the curators who has studied & written about diamonds, or someone from GIA, or the like. Are you simply wanting to find out "What's the largest cubic crystal I can readily find to purchase", or are you wanting to know, "What's the largest cubic diamond that's ever been found?"

Since (by such is my experience) cubic diamonds, though uncommon, do tend to be less clear and of poorer gem quality, at least that means that they are more likely to have been saved as specimens, and not cut up and faceted!

If you are interested, I can post a query about this on the MSA's members email listserv, and see if anyone among the group has an answer for you.

Pete Modreski

[Gail]

Jim
Love the photo of you and LOVE the MAD about minerals signature.


Jim and I are involved in MAD in the Dallas area.

[Jim]

To Pete:

Thanks for your offer, and I would appreciate any help you can offer on this. It's more than a simple academic question; I am trying to gauge the significance of a crystal I've reserved.

To Gail:

Hey girl! This is Jim Houran also from the MAD Dallas group -- as if you didn't know ;) Yes, Jim and Gail and I are all mineral buddies. I'll let the forum in on a little secret about Jim and Gail. As someone who has spent time with them in their home, I can attest that their collection is as superb as it looks in the pics, and they are as hospitable and enthusiastic about the hobby as they come across here and Mindat.

[Pete Modreski]

Jim, I'll post something on the MSA's member listserv, and see if anyone has any good info/comments/insight for you about cubic diamond specimens.

Pete

[lluis]

Hi, Jim/List

Nice your article about the scam in the Crater of Diamonds.

I suppose that you are an expert in diamonds!

By the way, there is any other place, apart from Argylle, where pink diamonds are found?
I do not know any other place, but.....(I did not know till recently that Plumbago Mine was a source for pink quartz, crystallized... :-( )

With best wishes

Lluís

[Jim]

I am no expert per se, but I do know that pink and red diamonds have been found outside of the Argyle Mine (Australia). In fact, there have been about three "red" diamonds reportedly found at the Crater of Diamonds (Arkansas, US) -- and I have seen one of these. The Argyle Mine simply boasts, to my understanding, the greatest prevalence of pinks in terms of ratio.

[lluis]

Good afternoon, Jim/List

Thanks for answer.
I know that there are red diamonds (I was caught by one red in the wondow of De Beers in Dam Square in Amsterdam; It surely come from any place in south of Africa. Pity I could not afford it ), but I am intrigued by the pink ones.
I find them different, like the pink fluorite.
Again, many thanks for the answer

Lluís

[Pete Modreski]

Hi Jim,

I've received several responses that will be of more or less help to you from people on the MSA listserv, to your question about cubic diamond specimens that I relayed. I don't think I have a direct email address for you, so I'll just post the key excerpts from them here. A few offered comments about how large the crystals are that are in museum collections, and others shared general info about the morphology. The last paragraph below, by Ichiro Sunagawa about how such diamonds grow, is interesting. Here we go:

"Years ago George Kennedy at UCLA was able to synthesize diamonds in perfect cubic form to some sizeable fraction of a carat. His idea was to sinter them into large chunks of solid diamond, but I never heard that that worked. These were all made by a "belt" apparatus. Kennedy also had a phase diagram showing what conditions were needed to form a cubic habit, as well as other habits. I haven't seen this stuff discussed in many years. However supposedly GE knew all about that too. Presumably the rareity in nature is related to the conditions relative to this phase diagram. For other info I would suggest contacting John Betts in NYC, who often offers many uncut diamonds for sale from his web site.
Glenn Waychunas, Berkeley

"Diamonds prefer the octahedral shape. A the Denver museum we have a diamond that is 1/2 inch square although it also has some octahedral faces and dodecahedral faces truncating the edges. I am sure that Diamond dealers could tell you about crystals larger than 1 inch.
Jim Hurlbut [DMNS volunteer]

"I think the best person to answer your questions would be Dr. Emmanuel Fritch (Emmanuel.Fritsch(at)cnrs-imn.fr).
Good luck,
Brendan Laurs

"We have a cube that is slightly more than a centimeter on edge.
Carl Francis [Harvard]

"Hi Pete: Twenty to twenty five years ago, yellow cubic non gem diamonds were common from what was then called Zaire. However, I never saw any larger than 2 or 3 mm. One unscrupulous dealer tried to sell them as Arkansas diamonds which are mostly rounded dodecahedral. Excalibur Minerals has a diamond web site. Art Smith

"Hi Pete, For cubic morphology diamonds I suggest you inquire at the
American Museum of Natural History in New York, George Harlow,
specifically (I'll copy him on this e-mail answer) or the Smithsonian. I
would ask this question at these museums since they seem to garner at
least eventually, most of the unique specimens no matter where found . I
believe Harry Winston donated some items (possible not diamonds) to the
Mineralogy collection there. George is most appropriate as I know he
mounts wonderful exhibits for the public and has been involved with the
'jade' question which brings him a broad acquaintence among gemologists
A least he can suggest to you further possibilities, I suspect. There is
also the Gemological Institute of America although I would think any
sensible person might recognize a cubic diamond as much more than a gem
Catherine Skinner [Yale Univ.]

Pete,
"Whereas there is a relationship between P-T growth conditions for synthetic diamonds relative to morphology (see Wilks and Wilks, 1991) or Bruton (1978), etc. has been known for a long time, the cubes I am most familiar with as natural diamonds are the highly decorated cubic overgrowths from the Democratic Republic of the Congo. We have such cubes up to 17 mm. Other than that, they will need to cope with the Kimberley Process for which much of Congo is not in compliance, as I understand it.
George Harlow [AMNH]

"Pete and George,
I have seen very few gem quality cubes as they tend to be fibrous, almost amorphous shaped crystals. Production out of Canadian mines may be your best bet at finding cubic diamonds. They have a high percentage of cube-shaped diamonds (many of them are cubo-octahedrons) of which some are non-fibrous cubes. I have seen some decent sized cubes from Siberia (~10 mm) as coated green and yellow stones.
Rondi Davies [connected with AMNH I think, or maybe not]

"Natural cubic (or more correctly cuboid) diamond experienced two growth stages, the earlier octahedral growth under low driving force condition, on which later fibrous growth took place under higher driving force condition. Their sizes are determined depending on how long cuboid diamonds experienced the seconnd stage. In natural crystallization, {100} exclusively behaves as a rough interface, and thus it is not crystallographically proper {100} face, whereas it behaves as a smooth interface in metal soution in HPHT synthetic diamond. Synthetic diamonds are bounded by {111} and {100}, both being crystallographic faces on which spiral growth is the principal growth mechanism. The difference between natural and HPHT synthetic diamonds in the growth of {100} is due to the difference in their solvents, which influences surface reconstruction of the face. These are discussed in my book, Sunagawa "Crystals, growth, morphology and perfection", Cambridge Univ. Press, 2005. Cheers Ichiro

Prof. Ichiro Sunagawa
Kashiwa-cho 3-54-2, Tachikawa,
Tokyo, 190-0004 Japan
TEL:+81-42-536-2564
FAX:+81-42-535-3637
e-mail:i.sunagawa(at)nifty.com

[Jim]

Hi Pete,

You ROCK! (pun intended). I recognize several of your contributors (like Brendan and Carl), and this is excellent information.

For my TN gem crystal collection, I just acquired an 11mm square, nicely translucent "silver" cubic/cuboid crystal from the Kasaï-Oriental province, southern-central Democratic Republic of Congo (Zaïre). It is much higher quality than a typical industrial grade diamond, which was a pleasant surprise!

In fact, it was such a nice piece that I was inspired to learn about comparable specimens. You've helped tremendously. I've more investigative work ahead obviously, but your generosity and helpfulness have paved the way for me.

Much appreciated!

[Pete Modreski]

Hi again Jim,

Thanks, and I'm happy to have been of help; I learned things too, it was a very productive question.
Your 11 mm "cuboid" crystal sounds quite good, and from the replies we have seen, sounds pretty well at the large end of what is obtainable. I have certainly had my knowledge level raised as to the difference between true cubic form growth, and "apparent" cubic form = "cuboid", though to be honest, I'm still not sure I completely understand this. I'm not much familiar with faces on minerals, that are logically permitted by their symmetry, being observed but being "not true growth faces"; I will have to think or read about this some more.

And by the way, in browsing some websites about diamonds, I came across the pictures posted of the details of the crystals in the Arkansas diamonds case from Tucson, and I realized how extensive your own diamond collection is, and how much of what was in that case was yours--congratulations, very good, first rate, a really nice collection! (Now that I just tried to go back to that and look again, I can't quite figure out what website I found that at.. was it from The Vug, or from Mindat, or from TGMS... neither of those seems to have it...).

And, here are several more postings I've received from MSA about the cubic diamonds question:

See: Max Bauer: "Precious Stones" (Dover Pubs.) which gives several facts on cubic (and other) diamonds.
The book by V. Mordechai (not Moritz) Goldschmidt devoted to diamond crystallography should be available somewhere on the web.
J.J. Jacques Jedwab <jjedwab>

I know little about macrodiamonds and hence what I have to say here may be irrelevant.
Our experience with microdiamonds, both those grown in sedimentary rocks and in our own experiments is that the true crystal faces they exhibit are octahedral -- even those that have a cubic external form. We described a way the latter can form in Dobrzhinetskaya et al., Geology 29:263-266.
Harry Green Harry Green <harry>

Hello Peter:
I'd like to add three points to the contributions made thus far:
[1] Cubic diamonds (senu stricto) are rare, but diamonds with cuboidal morphology are widespread, the notable difference being that the latter are fibrous, yellow from abundant N, cloudy, & laced with trapped hydrous minerals, carbonates and fluid inclusions with compositions considered to be typical of kimberlitic "magmas" (all other diamonds are mantle host rock related, dominantly peridotitic & eclogitic).
[2]The largest fibrous diamond I've seen is ~1cm. As George noted, some of the cuboids are overgrown on octahedral diamonds, hence paragentically later with fast fibrous growth & possibly related to pre-eruption crystallization on ancient diamond nuclei
[3]Diamonds have morphology-sensitive P-T stability regions: octahedra form at high P-T & cubes (sensu stricto) at slightly lower conditions. It's in the intermediate conditions that cubo-octahedra form, and i'ts the region of choice for synthetic diamond production because the number of coigns are increased and the cutting-edge points maximized.
Best regards, Steve.
Stephen E. Haggerty, Distinguished Research Professor, Dept. of Geosciences, Florida International University <haggerty>

An interesting lecture about this topic with title :
'Cubic growth of natural diamond '
was given by Moreton Moore (Roy. Holloway Univ. London) at the 23 rd European Crystallographic Meeting, 2006 - Leuven, Belgium, The abstract was published in Acta Cryst. (2006). A62, s65 with open access pdf file
https://journals.iucr.org/a/issues/2006/a1/00/issconts.html
greetings, Jan Elsen, Prof. dr. Jan Elsen, Katholieke Universiteit Leuven, Afdeling Geologie, Geo-instituut KULeuven Postbus 2410, Celestijnenlaan 200E - B-3001 Heverlee

[Jim]

Hi Pete,

Just when I think you can be any more gracious, you add more information and throw in some compliments as well!

I truly appreciate your comments about the AMT case. It was fun to organize that display -- almost as much fun as tracking down those AR diamonds!

While I collect other gem crystals, diamonds are especially fascinating to me. Colored diamond crystals are among the beautiful crystals in my opinion!

Cheers for now...

[Jim]

meant to say.. "...can't be any more generous...!"

This is what happens when you talk minerals while on allergy medication :)