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Contributions to Mineralogy and Petrology

, Volume 39, Issue 2, pp 103–116 | Cite as

The discovery of garnets closely related to diamonds in the Finsch pipe, South Africa

  • J. J. Gurney
  • G. S. Switzer
Article

Abstract

Magnesium-rich, calcium-poor, lilac coloured garnets have been found in the heavy mineral concentrate of the Finsch kimberlite pipe. Some of these garnets contain sufficient chromium to place them within the compositional field of the garnets previously only reported as inclusions in diamonds.

These lilac garnets are considered to have formed in equilibrium with the minerals found as inclusions in diamond and hence with the diamond itself. Their presence in the kimberlite should be diagnostic of the presence of diamond, but it is not known if there is any quantitative relationship. The garnets are considered to have a deeper provenance than the magnesian garnets commonly found as xenocrysts in kimberlite and in garnet peridotite xenoliths. The mantle composition at their depths of origin must be more refractory in nature than the peridotite xenoliths. The garnets having a higher magnesium and chromium content, a higher Mg/Fe ratio and lower calcium, aluminium and titanium than those found in the xenoliths.

Keywords

Calcium Aluminium Titanium Magnesium Chromium 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag 1973

Authors and Affiliations

  • J. J. Gurney
    • 1
  • G. S. Switzer
    • 2
  1. 1.Department of GeochemistryUniversity of Cape TownRondeboschSouth Africa
  2. 2.Department of Mineral SciencesSmithsonian InstitutionUSA

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