Cation Disorder Caused by Olivine-Ringwoodite Phase Transition Mechanism, Possible Explanation for Blue Olivine Inclusion in a Diamond

Round 1

Reviewer 1 Report

The paper is undoubtedly interesting and it relates to one of today´s most active new branches of research, providing very illustrative figures based on the results obtained by a modern instrumental equipment. Therefore, there is a need to publish the study. As there are still some issues that are to be addressed, my overall recommendation is Minor revision prior to its publication.

Specific comments and suggestions

It is a pity that the paper does not include Graphical Abstract. The manuscript contains some very illustrative figures, in my opinion, some of them could be used for its preparation (which could further enhance the impact of the paper).

There is no doubt that information contained in introduction is interesting. Despite this, more attention could be paid to description of current knowledge background, challenges and knowledge gaps. Then, at the end of the introduction, the aims of the paper could be clearly stated within the last paragraph (and joined with the knowlegde gaps described above).

Line 345: Please correct [18,19,20,21,22] to [18-22]

Conclusions. Even if described in section Implications, the most important ones could be mentioned also within the conclusions (busy readers often do not read the whole paper in detail but only look at some figures, tables or conclusions).

At the end of the manuscript: It is a question whether to repeat the authors´ contribution also in special section (it is described in detial within the text); but at least the Funding information should be provided - if there was no funding, "This research received no external funding" should be mentioned.

 

Author Response

Reviewer 1

It is a pity that the paper does not include Graphical Abstract.

The authors do not think a graphical abstract is needed because the figures in a digital paper are so readily available.

There is no doubt that information contained in introduction is interesting. Despite this, more attention could be paid to description of current knowledge background, challenges and knowledge gaps. Then, at the end of the introduction, the aims of the paper could be clearly stated within the last paragraph (and joined with the knowledge gaps described above).

The authors opted not to address this because we feel it is not needed.

Line 345: Please correct [18,19,20,21,22] to [18-22]

Thank you for pointing this out. We have corrected it.

 If there was no funding, "This research received no external funding" should be mentioned

We have added it.

Reviewer 2 Report

Dear Authors:

 

In my viewpoint, the manuscript titled “Cation Disorder Caused by Olivine-Ringwoodite Phase Transition Mechanism, Possible Explanation for Blue Olivine Inclusion in a Diamond” can be accepted to publication after major revision.” This ranking can be justified as follow. For a direct indexing of major topics that can be reviewed, I will approach each major topic containing suggestions, in the order of manuscript.

However, I would like some previous comments, prior to entrance in the suggestion list; I would like make two or three suggestions steaming organization and characteristics of manuscript. First, I suggest to author to write in impersonal form, instead of third person, “we”.  See, a text constructed in impersonal way seems far from a testimonial. When authors use “we”, seems that text’s manuscript undergo a bump. See in the sequence, a part of manuscript, where in a couple of lines “we” appear four times, see: …“We also examined the inter-141 mediate diffraction patterns not only by quenching, but also by observing multiple pat-142 terns obtained by energy spectra during progress from step 1 to step 2. We then plotted ratios of intensities of emerging γ-phase miller indices (331):(400), which is insensitive to cation ordering and in contrast (440):(400), which is sensitive to cation ordering between step 1 and step 2 (Figure 4). We chose to plot areas under the peaks because they are more accurate indicators of intensities than peak heights. Using the series of synchrotron diffraction patterns collected between step 1 and step 2 employing our selsyn method for obtaining pressure increase with very small increments, we interpreted the data shown in graphs Figures 4a and 4b. Neither of these ratios depends on the absolute quantities of either α or γ phase.”… All times I felt a rupture of continuity.

In the same way, I suggest to cut off must part of adverbs along of text’s manuscript. It’s possible that such strategy is interesting in a talk but in a text of paper the improvement in the transport of information nonexistent. Well, if text is of scientific type, adverbs aren’t necessaries. As an example, in the text:..“We chose fayalite, the iron-rich endmember of the olivine series (because its transition pressure is the lowest in the olivine series). It “immediately” became apparent that the phase transition from the olivine structure, α Fe2SiO4, to ringwoodite’s spinel structure, γ Fe2SiO4, took place in two steps when pressure was “gradually” increased. In each run we were pleased to find that we were able to record the diffraction pattern of sample intermediate between step 1, the displacive sliding of the layers of oxygen atoms, and step 2, the diffusion of cations to the “newly” established sites in the spinel structure, by quenching the sample to 25°C “approximately” midway between the two steps. This allowed us to obtain Debye-Scherrer diffraction patterns of all three stages and mount them side by side so direct visual comparisons could be made (Figure 3). The fact that Fe2SiO4 also transforms by disproportionation to wustite (FeO) + stishovite (SiO2) mixture at a still hig…”.

At end, I would comment that for a manuscript, in some places there is a strange narrative of historical focus involving places, persons and physiologic features of some persons. As previously mentioned, this isn’t necessary in a paper, fortunately additional file can be provided to maintain and divulge this in time. As an example, “of Elise’s ongoing collaboration with her co-author, Bill, John approached his friend to offer her the”…and  … “During the next few years after Elise accepted John Koivula’s challenge,”…and

… “colleague and friend, Steven D. Jacobsen, to make a foursome of John I. Koivula, Elise, Bill, and Steven Jacobsen. Steve is responsible along with his colleagues for the beautiful”…

 

Title

The item Title as ist is double, At moment, in my view, there at two Titles. In this sense, I suggest to authors one of most interesting title that I saw that is “Explanation for Blue Olivine Inclusion in a Diamond”. From my inspection, This model is a single at moment and should be strong by several decades. I understood the presence of word “Possible” in the original tentative title. Then, I suggest that move the word “possible” for the body of the manuscript. However, first of all, it’s necessary to solve information reported at second part of the Conclusion item that weakened all modeling.

 

Results

Some legends of Figures is too long, Due to long text, seems that text formatting lost the best level. Then, I suggest that significant part of legends be moved to text of manuscript. This is the case of legends ascribed to Figures 3, 5, 5, 8, 9, 11, 12, 13, 16 and 17.

I suggest to delete the comment …”We can’t help thinking that sliding one layer over another would be like riding on the rumble strip of a highway, or better yet like rolling a large rock on a set of irregular logs such as a block on its way to a pyramid or perhaps an Easter Island moai on its way to a pedestal by the coast.”…This comment contains some excess of information that is not pertinent to idea necessary.

As suggestion, delete the Fig. 10…“Figure 10. Illustration of step 1 of the shear-induced displacive restacking of the oxygen layers.”

 

Conclusion

I suggest that all items be re-written. In this manuscript, seems that the item conclusion is connected with item Title. Then, the relevance of Title is antagonistic with relation conclusion.

 

As an additional suggestion an approach more assertive of “model” should be structured. In this sense, o model “per si” seems robust for explain a specific set of phase-transitions. In this sense, seems that direct and inverse phase-transition would be unified. The model seems consistent and can be used to explain some set of phase-transitions. Then, the inverse aspect and its correlation with model should be previously detailed.

 

Reference

 

The sequence of references should be turned express in a proper file, indexed to the manuscript, see rules of the Journal:

 

9. Ito, E. (Okayama University, Misasa, Japan). Personal communication, 1991.
10. Rubie, D.C. (Bayerisches Geoinstitut, University of Bayreuth, Germany). Personal communication, 1994
11. Yagi, T.M., (University of Tokyo, Japan). Personal communication, 1991.
12. Jacobsen, S. D., Northwestern University personal communication, 12/11/2020.

 

Author Response

Reviewer 2

 I suggest to author to write in impersonal form, instead of third person, “we”

Both authors strongly believe that scientific writing can benefit from a more casual and conversational style in which the authors and their colleagues use the first-person singular and plural so the reader can better follow the thought process involved in the research.

 If text is of scientific type, adverbs aren’t necessary

The authors wish to use adverbs appropriately and are concerned about the tendency for English speakers to substitute adjectives where adverbs are appropriate. We try to resist this trend.

There is a strange narrative of historical focus involving places, persons and physiologic features of some persons

The authors think that readers, especially those familiar with some of the participants, might be interested in their roles.

Line 64-66. “A number of researchers have employed ways to achieve shear stress”. References are needed.

We have limited this to our own experience and solutions and have removed reference to other researchers.

Line 200. What do you mean with “if the cations are to know where to go”?

The authors think this casual terminology is appropriate for the tone of the manuscript and we have not made changes to remove this.

It is a question whether to repeat the authors´ contribution also in special section (it is described in detail within the text). Thank you.

The authors decided to give more information about the authors at the end in the “Author’s Contributions” section.

Reviewer 3 Report

The paper presents an extensive overview on the olivine-ringwoodite transition in olivines of several compositions using synchrotron X-ray diffraction and visual observations in a diamond anvil cell. New insights on the discovery of blue olivine in diamonds are provided. The methodological approach provide a good viewpoint on the structural changes occurring during olivine-ringwoodite transition. Overall the study is high quality. The paper is a comprehensive overview of excellent academic accomplishments that first author and collaborators achieved over the years. I see a better fit as a review paper rather than an original research article. I suggest the publication with minor revision.

Please consider the comments below to revise your manuscript:

1. Line 64-66. “A number of researchers have employed ways to achieve shear stress”. References are needed.
2. Line 200. What do you mean with “if the cations are to “know where to go”.”?
3. Line 215-218. Is this example necessary?

Author Response

Reviewer 3

Line 215-218. Is this example necessary?

The authors think it is necessary

Line 64-66. “A number of researchers have employed ways to achieve shear stress”. References are needed.

We have limited this to our own experience and solutions and have removed reference to other researchers.

Line 200. What do you mean with “if the cations are to know where to go”?

The authors think this casual terminology is appropriate for the tone of the manuscript and we have not made changes to remove this.

“I see a better fit as a review paper rather than an original research article. I suggest the publication with minor revision”.

Reviewer 3 is right that much of the text reviews earlier research. However, the authors believe that that earlier research has enabled them to answer a very puzzling question concerning the origin of an enigmatic blue olivine crystal. This is a promising new explanation for a discovery of a blue inclusion in a diamond. We hope that our colleagues who conducted such detailed research into the nature of the origin of the blue inclusion will provide a report of their own about the many steps taken in search of a comprehensive explanation.

Reviewer 4 Report

I liked very much the work and I think that such work (very different from the common way to write a paper, providing an extremely interesting historical overview) must be published. Here below I report some very minor issues. However, there are a couple of points that, as an expert of inclusions in diamonds, I should point out:

1) I like the elegant way to explain that the blue olivine in diamond could be the back transformation from an original ringwoodite and I must admit that I don’t have any other alternative explanations by now. However, we must not neglect the diamond host. If the blue olivine is the back transformation from ringwoodite, then the diamond host must be a super-deep diamond. We all know very well super-deep diamonds and they have specific features like a completely irregular shape, strong plastic deformation features, very low or no nitrogen content. So, if I understood well, it is impossible now to know such information about the diamond host in Figure 12. Especially the nitrogen content by FTIR would have been a super important information to discriminate a super-deep diamond from a lithospheric diamond. The diamond in Figure 12 appears like a typical lithospheric diamond.

2) Other inclusions in diamond in Figure 12. The reddish inclusion is reported to be pyrope and I agree, typical pyrope in diamond. However, if this is a super-deep diamond, such pyrope would be indeed a majoritic garnet. I wonder if there is any chance to analyse the composition of the pyrope to check the Si excess typical of majoritic garnets. In diamonds, this is found in several cases (see for example, Smith et al. 2018, Nature, 560, pages 84–87 and others) and is a very robust evidence of super-deep origin. At the same time, it would be extremely important to know which kind of inclusions are the colorless crystals in Figure 12 close to the blue olivine. Even a super-quick Raman analysis would give such information. For example, it is now established that in super-deep diamonds we can find low-Ni enstatite and when coexistent with ferropericlase and/or ringwoodite they are considered back-transformation from bridgmanite. Which inclusions are these? Are simply colorless olivines or enstatites? If they are colorless olivines, why do we have blue and colorless olivines at only a few microns of distance (the small colorless inclusion is at about 60-70 micron from the blue olivine)? The colorless inclusion on the top of the blue one is quite huge indeed and could be easily measured by diffraction or microRaman in a few minutes.  

Said this, even if the authors will be not able to provide such data, I think that the work should be published but in this case I clearly ask that they mention that their interpretation could be definitively correct but at the same time could not be correct based on the above points 1 and 2.

 

Here below just a few minor comments:

- a quick question: did you test for cobalt presence in such olivine? It is known that cobalt in synthetic forsterite give a very intense blue. For example, for Mg1.8Co0.2SiO4 composition, you get deep blue olivine (e.g., El Hadri et al. 2015, Journal of the European Ceramic Society 35 (2015) 765–777), however, in natural olivine it is impossible to get such large amount of cobalt. At the same time, the blue color of the olivine in Figure 12 is indeed a quite light blue color and I would not definitively exclude that small amount of cobalt could cause it. For example, we know that olivines in diamonds can reach up to CoO 0.03% wt (see Sobolev et al. 2008, EJM, 20, 305). Let me be clear, I don’t believe much in this possibility but I just wonder if the authors tried to measure even cobalt given that in synthetic samples cobalt is the main blue color cause in olivine.

- It would be better call Fe2SiO4 ringwoodite with its actual mineral name which is now “ahrensite” citing the following paper: Ma et al. (2016) Geochimica et Cosmochimica Acta: 184: 240-256.

- Sorry, section 3.2.1. At line 172, there is something missing over here. It seems that the sentence starts but has not any ends. Then the text restarts at line 194 but it is here another section starting.

-Section 4, indeed the authors should widen the chemical variability as recently the Fe-analogue of wadsleyite has been found. See the new mineral asimowite (Bindi et al. 2019, American Mineralogist, v. 4, doi: 10.2138/am-2019-6960)

Author Response

Reviewer 4

We thank reviewer 4 for his complimentary comments and very useful suggestions.

If the blue olivine is the back transformation from ringwoodite, then the diamond host must be a super-deep diamond

Based on the following information, we believe that the diamond was formed in the upper mantle and not formed super deep. FTIR spectra of the diamond indicate a nitrogen content of 91 ppm. That and the presence of A nitrogen aggregates indicates that it likely formed in the upper mantle. In addition, the presence of olivine and lack of ferropericlase also indicate upper-mantle/lithospheric origin.

The reddish inclusion is reported to be pyrope and I agree, typical pyrope in diamond. However, if this is a super-deep diamond, such pyrope would be indeed a majoritic garnet. I wonder if there is any chance to analyze the composition of the pyrope to check the Si excess typical of majoritic garnets. 

Concerning the red garnet:  Single-crystal X-ray diffraction data and X-ray fluorescence indicate chrome pyrope thus confirming the identification of chrome pyrope by John Koivula, also indicating an upper-mantle origin. All of these observations support pyrope instead of majorite for the red inclusion.

At the same time, it would be extremely important to know which kind of inclusions are the colorless crystals in Figure 12 close to the blue olivine. Even a super-quick Raman analysis would give such information. If they are colorless olivines, why do we have blue and colorless olivines at only a few microns of distance (the small colorless inclusion is at about 60-70 micron from the blue olivine)? 

The colorless crystals have been analyzed by Raman and by XRD and have been confirmed to be olivine. Their lack of color may be due in part to their smaller size and partly due to more rapid equilibration of temperatures during the gamma-alpha transition, again due to their smaller size. We have added additional descriptive text to the manuscript describing the reason for lack of color. In that discussion we propose that the small sizes may lead to a more rapid progression of the reverse phase transition thereby leading to completion at a higher temperature giving more chance for step 2 to go to completion.

Did you test for cobalt presence in such olivine? I just wonder if the authors tried to measure cobalt given that in synthetic samples cobalt is the main blue color cause in olivine.

Our chemical analysis of the blue inclusion by XRF was added to the text as Table 3 and shows a negligible amount of cobalt.

It would be better call Fe2SiO4 ringwoodite with its actual mineral name which is now “ahrensite” citing the following paper: Ma et al. (2016) Geochimica et Cosmochimica Acta: 184: 240-256.

We added discussion of the mineral ahrensite along with wadsleyite as Section 4 (Line 311-323)

Sorry, section 3.2.1. At line 172, there is something missing over here. It seems that the sentence starts but has not any ends. Then the text restarts at line 194 but it is here another section starting.

A sentence was inserted following the header for section 3.2.1 that describes the purpose of Figures 6-8.

Section 4, indeed the authors should widen the chemical variability as recently the Fe-analogue of wadsleyite has been found. See the new mineral asimowite (Bindi et al. 2019, American Mineralogist, v. 4, doi: 10.2138/am-2019-6960)

New text has been added to section 4 to introduce asimowite.

Round 2

Reviewer 2 Report

From my viewpoint are clear further efforts from part of authors to improvement of manuscript. The paper can be accepted to publication.