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Evidence for two blue (type IIb) diamond populations

Nature volume 570, pages E26–E27 (2019)Cite this article

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Matters Arising to this article was published on 12 June 2019

The Original Article was published on 01 August 2018

arising from: E. M. Smith et al. Nature https://www.nature.com/articles/s41586-018-0334-5 (2018)

Blue type IIb diamonds owe their colour to the presence of low concentrations (about 0.01–10 parts per million)1 of boron. It has been argued, on the basis of their inclusions, that these rare stones are all derived from the lower mantle (at depths of about 600 km)1. Limited new carbon-isotopic data presented by ref. 1 were interpreted to complement earlier analyses of blue type II diamonds, collectively reflecting a range of light-to-heavy carbon-isotopic signatures. Our analysis indicates that type IIb diamonds instead represent two isotopically distinct parageneses with contrasting inclusions, one indeed derived from the lower mantle, and the other linked to the websteritic suite, and therefore of lithospheric provenance.

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Fig. 1: Size-class distribution of the different inclusion associations in the blue diamonds documented by Smith et al.1 (see text for discussion).
Fig. 2: Comparison of carbon-isotopic signatures of Type IIa (CLIPPIR5) and blue IIb diamonds from Cullinan-documented10 and type IIb stones of the Ca- and Mg-associations respectively, documented by Smith et al.1.

Data availability

All data are from Smith et al.1 and cited sources.

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Acknowledgements

We thank T. Stachel for constructive comments. We thank S. Abraham for producing the figures.

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Authors and Affiliations

  1. Department of Geology, Rhodes University, Grahamstown, South Africa

    Andy E. Moore

  2. School of Earth and Ocean Sciences, Cardiff University, Cardiff, UK

    Andy E. Moore

  3. Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, Ontario, Canada

    Herwart Helmstaedt

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  1. Andy E. Moore
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The authors collaborated closely in the formulation and writing of this manuscript.

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Correspondence to Andy E. Moore.

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Moore, A.E., Helmstaedt, H. Evidence for two blue (type IIb) diamond populations. Nature 570, E26–E27 (2019). https://doi.org/10.1038/s41586-019-1245-9

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