Non-Metamict Aeschynite-(Y), Polycrase-(Y), and Samarskite-(Y) in NYF Pegmatites from Arvogno, Vigezzo Valley (Central Alps, Italy)
, Fabrizio Nestola 1, Mariangela Schiazza 3, Milan Novák 2 and Giorgio Pennacchioni 1Round 1
Reviewer 1 Report
Please allow me to write a review for this very important, interesting and valuable manuscript which is very suitable to “Minerals” reporting attractive research area of “Non-metamict aeschynite-(Y), polycrase-(Y) and samarskite-(Y)”. The contents in this paper are certainly novel and the quality of the work is high. The technical validity of the characterization work is good. This work will be of interest to members of minerals communities. I feel that the authors are expert in these related fields and I can confirm that the characterizations appear to be very well carried out. I am very happy to recommend publication as original paper in the special issue of “Minerals”. The authors may wish to take into account the following points when putting together a final, publishable, version of the manuscript.
1) As to Chemical compositions such as the line 106, 148 and 167, would the authors please describe in details how to determine how contents U and Th of actinides are?
2) Would the authors please describe in details what and how important U and Th are, being compared to REE?
3) As to the line 122, would the authors please describe in details the oxidation states of Fe3+ and Mn2+? How did the authors determine the oxidation sates? Are there any possibilities of Fe2+ and Mn3+? Are there 57Fe Mossbauer spectroscopy investigations for the related research area?
I feel that I would like to see “57Fe Mossbauer spectra” for the minerals in this paper in future.
4) As to the line 244 and 245, I feel that U6+ is also stable as U4+. How about U6+?
5) Would the authors please describe more in details what most highlight points are in this valuable Table 1 in order to be understood easily?
Author Response
Referee 1
Please allow me to write a review for this very important, interesting and valuable manuscript which is very suitable to “Minerals” reporting attractive research area of “Non-metamict aeschynite-(Y), polycrase-(Y) and samarskite-(Y)”. The contents in this paper are certainly novel and the quality of the work is high. The technical validity of the characterization work is good. This work will be of interest to members of minerals communities. I feel that the authors are expert in these related fields and I can confirm that the characterizations appear to be very well carried out. I am very happy to recommend publication as original paper in the special issue of “Minerals”. The authors may wish to take into account the following points when putting together a final, publishable, version of the manuscript.
1) As to Chemical compositions such as the line 106, 148 and 167, would the authors please describe in details how to determine how contents U and Th of actinides are?
2) Would the authors please describe in details what and how important U and Th are, being compared to REE?
CORRECTED TEXT : According to the IUAPC (International Union for Pure and Applied Chemistry), the term rare earth elements (REE) include lanthanoids (Ln), yttrium (Y) and scandium (Sc). Due to the substantially smaller ionic radius of Sc with respect to the rest of group, it frequently enters different crystal-structural sites via different substitutions and therefore the Sc is commonly not included as REE in geological sciences neither in this paper. Due to the lanthanide contraction phenomena, the REE are further divided to larger LREE (light Ln, La-Gd) and smaller HREE (heavy Ln, Tb-Lu). Th4+ and U4+ show similar behaviour respectively having 0.94 Å and 0.89 Å ionic radius.
3) As to the line 122, would the authors please describe in details the oxidation states of Fe3+ and Mn2+? How did the authors determine the oxidation sates? Are there any possibilities of Fe2+ and Mn3+? Are there 57Fe Mossbauer spectroscopy investigations for the related research area?
I feel that I would like to see “57Fe Mossbauer spectra” for the minerals in this paper in future
CORRECTED TEXT: The Fe and Mn oxidation state was determined in samarkites by bond valence calculation following Britvin et al. [8]. Taking into consideration that AGM and EGM group minerals have sensible iron contents, future Mossbauer spectra may discriminate and quantify the amounts of Fe3+ and Fe2+.
4) As to the line 244 and 245, I feel that U6+ is also stable as U4+. How about U6+?
ANSWER: U6+ in six fold coordination has 0.73 Å ionic radius which is too small if compared to U4+ (0.89 Å)
5) Would the authors please describe more in details what most highlight points are in this valuable Table 1 in order to be understood easily?
CORRECTED TEXT: Table 1 has been fullyr eorganized
Reviewer 2 Report
The paper reviewed contains a lot of new data and will be interesting for mineralogists, geochemists, crystal chemists and specialists who study origin of granitic pegmatites and rare-element mineralization in them. It should be specially noted that the described rare-earth titano-niobates are crystalline that is very rare in nature, especially for samarskite. Thus, the work makes significant contribution in their mineralogy and crystallography.
The paper could be published in "Minerals" after minor revision. In particular, the data on samarskite-(Y), which are in some contradiction to each other in different parts of the paper, should be improved and aligned with modern data (see [8]).
The comments are as follows.
Tables 1 and 2. The presence of Si in these minerals seems very doubtful: no reasonable structural position for Si, even as minor admixture, could be suggested. In my mind, it could be a result of error in EMPA due to the overlap of analytical X-ray lines of Si (K) and Ta (M). I would recommend to revisit the analyses in part of Si: is it real admixture in these oxides or an artefact?
Table 2. Fe should be re-calculated to Fe2O3 that is more correst for samarskite (and analytical totals will be increased for almost 1 wt.%). "FeOtot" is in contradiction with crystal chemical data for samarskite and, in particular, with the statement written at page 4, line 170.
Table 2. It seems more probable that Sc is located in the B site rather the A site due to its crystal chemical similarity to Fe3+ rather Y and majority of lanthanides (see also chapter 4.4). However, this is questionable point and cannot be clearly solved here due to low content of Sc. Thus, I don't insist on the shifting of Sc from B to A.
Table 3. It seems reasonable to include the data on non-metamict samarskite-(Y) from [8] (Britvin e.a., 2019), the only structure data for natural samarskite (and the only data for samarskite with space group determined).
The actual full reference for [8] (published online) is: Britvin S.N., Pekov I.V., Krzhizhanovskaya M.G., Agakhanov A.A., Ternes B., Schüller W., Chukanov N.V. (2019) Redefinition and crystal chemistry of samarskite-(Y), YFe3+Nb2O8: cation-ordered niobate related to a family of layered double tungstates // Phys. Chem. Miner. DOI: 10.1007/s00269-019-01034-0
Page 10, lines 121-124. Samarskite typically contains H2O. However, how vacancies in the B site are connected with low analytical total? This should be explained more clear (at least, as in Discussion).
Page 13, lines 224-227 and page 15, lines 299-301. The statement is incorrect: see [8].
Page 15, lines 294-295. The data are obsolete (see [8]) and should be deleted or replaced by data corresponding to the present-day state of knowledge on samarskite.
Abstract seems not too good. It contains very few mineralogical data (given formally), which are the major material in the paper, and is significantly focused on geological points, including geological age which is not a result of the present work. Also it would be desirable to avoid abbreviations in Abstract (AGM, EGM, SCXRD). Thus, Abstract should be deeply revised.
Page 2, line 56: change Ilfeld to Eifel.
Page 7, line 12: of aeschynite-(Y), polycrase-(Y)
Table 3. Decimal point should be dot, not comma. And, Greek letters should not be italicized.
Author Response
Referee 2
The paper reviewed contains a lot of new data and will be interesting for mineralogists, geochemists, crystal chemists and specialists who study origin of granitic pegmatites and rare-element mineralization in them. It should be specially noted that the described rare-earth titano-niobates are crystalline that is very rare in nature, especially for samarskite. Thus, the work makes significant contribution in their mineralogy and crystallography.The paper could be published in "Minerals" after minor revision. In particular, the data on samarskite-(Y), which are in some contradiction to each other in different parts of the paper, should be improved and aligned with modern data (see [8]).
The comments are as follows.
Tables 1 and 2. The presence of Si in these minerals seems very doubtful: no reasonable structural position for Si, even as minor admixture, could be suggested. In my mind, it could be a result of error in EMPA due to the overlap of analytical X-ray lines of Si (K) and Ta (M). I would recommend to revisit the analyses in part of Si: is it real admixture in these oxides or an artefact?
ANSWER: Following the WDS analysis performed by Skoda we assumed lines SiKα and TaMα were well separated and any interference was avoided. For such reason we trust the date we obtained
Table 2. Fe should be re-calculated to Fe2O3 that is more correst for samarskite (and analytical totals will be increased for almost 1 wt.%). "FeOtot" is in contradiction with crystal chemical data for samarskite and, in particular, with the statement written at page 4, line 170.
ANSWER: WDS chemical analysis give FeOtot. In order to avoid artefacts showing high analytical totals we avoided to multiply FeO by 1.11 to Fe2O3. When apfu calculation was performed we calculated Fe2+ for aeschynite-(Y) and polycrase-(Y) and Fe3+ for samarskite-(Y) according to the data obtained from our study and from recent bibliography.
Table 2. It seems more probable that Sc is located in the B site rather the A site due to its crystal chemical similarity to Fe3+ rather Y and majority of lanthanides (see also chapter 4.4). However, this is questionable point and cannot be clearly solved here due to low content of Sc. Thus, I don't insist on the shifting of Sc from B to A.
ANSWER: Ok, we do not shift Sc
Table 3. It seems reasonable to include the data on non-metamict samarskite-(Y) from [8] (Britvin e.a., 2019), the only structure data for natural samarskite (and the only data for samarskite with space group determined).
ANSWER: Ok, we added crystallographic data from Britvin et al. in the table 3
The actual full reference for [8] (published online) is: Britvin S.N., Pekov I.V., Krzhizhanovskaya M.G., Agakhanov A.A., Ternes B., Schüller W., Chukanov N.V. (2019) Redefinition and crystal chemistry of samarskite-(Y), YFe3+Nb2O8: cation-ordered niobate related to a family of layered double tungstates // Phys. Chem. Miner. DOI: 10.1007/s00269-019-01034-0
ANSWER: Ok we added DOI in bibliography
Page 10, lines 121-124. Samarskite typically contains H2O. However, how vacancies in the B site are connected with low analytical total? This should be explained more clear (at least, as in Discussion).
CORRECTED TEXT: Low analytical totals measured for Bosco3 and Bosco4 samarskites show vacancy at the Mn2+ and Fe3+ site and this could be charge balanced by the entrance of OH- respect O2-. According to Britvin et al. [8] the sum of Fe and Mn in the M group is less than 1.0 apfu indicating the possibility of incomplete occupancy (vacancies) in the M site
Page 13, lines 224-227 and page 15, lines 299-301. The statement is incorrect: see [8].
Page 15, lines 294-295. The data are obsolete (see [8]) and should be deleted or replaced by data corresponding to the present-day state of knowledge on samarskite.
CORRECTED TEXT: Ok we added in addition to the very recent cell data obtained by crystal structure solved by Britvin et al. [8].
Abstract seems not too good. It contains very few mineralogical data (given formally), which are the major material in the paper, and is significantly focused on geological points, including geological age which is not a result of the present work. Also it would be desirable to avoid abbreviations in Abstract (AGM, EGM, SCXRD). Thus, Abstract should be deeply revised.
ANSWER. We have modified and implemented the abstract with additional mineralogical data.
Page 2, line 56: change Ilfeld to Eifel.
OK
Page 7, line 12: of aeschynite-(Y), polycrase-(Y)
Ok
Table 3. Decimal point should be dot, not comma. And, Greek letters should not be italicized.
Ok
Reviewer 3 Report
The article by Guastoni et al. is a good contribution to mineralogy and crystal chemistry of tantalo-niobates. It can be accepted for publication after addressing the questions raised during review. I would not say that it requires major review, but the raised questions would require appropriate disussion. Please look at the attached file.
Comments for author File: 
Comments.pdf
Author Response
Referee 3
The paper by Guastoni with coauthors reports on the detailed mineralogical study of a suite of
rare-earth minerals from the famous Alpine localities in Vigezzo Valley. The most interesting
aspect of this work (as it is highlighted in the title of the article) that the studied minerals are
non-metamict and thus could be studied in its pristine state using X-ray diffraction techniques.
This is, altogether with the good quality electron microprobe data, makes the authors’ findings
very important in view of the general crystal chemistry and mineralogy of tantalo-niobates.
Therefore, the article obviously deserves publication in the Minerals but, to my opinion, requires
some revision in view of the very recent structural data on Samarskite-(Y). The article by Britvin
et al. (2019) has been recently published (DOI: 10.1007/s00269-019-01034-0), thus the relevant
discussion would improve the quality of the manuscript.
1) Guastoni et al. shows that the studied REE-minerals form Vigezzo Vallye are not affected
to secondary alteration, therefore low totals of (Fe,Mn) in samarskite-(Y) (Table 2) might
indicate incomplete occupancy of (Fe,Mn) (M) site. The relatively low totals of M-site in
samarskite-(Y) from Eifel and Urals were discussed in the paper by Britvin et al. (2019).
Taking into account that many literature analyses of samarskite-(Y) show low M-site
contents, this aspect deserves special discussion. In this respect, the calculations based on
2 (Nb,Ta,Ti) apfu used by Guastoni et al. look very reasonable. Please extend this part of
discussion (lines 107, 116, 121-124 on page 10) in comparison with the structural and
chemical data published by Britvin et al. (2019).
CORRECTED TEXT: Low analytical totals measured for Bosco3 and Bosco4 samarskites show vacancy at the Mn2+ and Fe3+ site and this could be charge balanced by the entrance of OH- respect O2-. According to Britvin et al. [8] the sum of Fe and Mn in the M group is less than 1.0 apfu indicating the possibility of incomplete occupancy (vacancies) in the M site.
2) Table 3 (page 7); lines 214-218 (page 13). This is an important question which has to be
addressed in the revised manuscript. The authors give the unit cell metrics for samarskite-
(Y) from Bosco 3 without space group determination. The quality of X-ray data was not
sufficient for structure determination of samarskite-(Y). Britvin et al. (2019) have shown
that Sugitani et al. (1985) and all succeeding authors gave a wrong cell setting for
samarskite-(Y) which is incompatible with its crystal structure. It seems that Guastoni et
al. (page 13, lines 217-218) also refers to the wrong cell setting first introduced by
Sugitani et al. (1985). Please resolve this question in the revised version of the
manuscript.
CORRECTED TEXT: Ok, we added crystallographic data from Britvin et al. in the table 3 and we modified our cell setting according to Britvin et al., 2019
3) Line 224-227 (Page 13). This is not true (but the authors, indeed, could not be
acknowledged with these, very recent data). The structural determination of samarskite-
(Y) from Laacher See by Britvin et al. (2019) was performed on the untreated (natural)
crystal at room temperature. However, the structural data by Guastoni et al. are important
in view of the overall genesis of samarskite-(Y) because they are collected from the
crystal of pegmatitic origin. In this respect, the proper resolution of the cell metrics (see
the preceding question) would be very appreciable.
CORRECTED TEXT: Bosco3 samarskite-(Y) is the first crystal from pegmatites for which cell data were obtained by SCXRD technique at room temperature following the cell data of samarskite-(Y) occurring in sanidinites from Laacher See published by Britvin et al. [8].
4) Lines 234-245 (Pages 213-214). Thes e isomorphous substitutions are discussed by
Britvin et al. (2019).
CORRECTED TEXT: As far as Bosco3 and Bosco4 samarskite-(Y) is concerned, the trend is rather homogeneous and exchange vectors considered can be represented and described by Britvin et al. [8] as follows:
Ca2+ +U4+ ↔ 2(Y, Ln)3+
U4+ + Ti4+ ↔ (Y, Ln)3+ + Nb5+
5) Conclusions (Lines 299-302, page 15). Please discuss these topics according to the
previous questions.
CORRECTED TEXT: AB2O6 oxides from Arvogno have the ionic exchange Fe2++(Nb+Ta)5+ à (Y3++ REE3+)+Ti4+ mainly regulates the compositional transition from ABX2O8 samarskite-(Y) to polycrase-(Y) and aeschynite-(Y) with AB2O6 crystal structure. According to Britvin et al. [8] the thermal behavior of metamict samarskite-group minerals never result in complete restoring of original, pre-metamict crystalline phase
Some minor remarks:
Page 6, line 9. Please give proper reference for CrysAlisPro software.
OK
Page 8, line 37. IUPAC (not IUPACH)
OK
Page 16, ref. 8 (lines 370-372) Please add DOI forthe published paper:
10.1007/s00269-019-01034-0.
OK
Sincerely,
Round 2
Reviewer 3 Report
Dear Dr. Guastoni,
Please, introduce one more minor correction in the first sentence of the Conclusions chapter (lines 486-487):
Previous crystallographic data from literature of samarskite from pegmatites [3-4,6] were always obtained by XRPD (X-ray powder diffraction) and this is the first study where cell data of samarskite-(Y) from pegmatites were obtained by SCXRD at room temperature.
