Enigmatic super-reduced phases in corundum from natural rocks: Possible contamination from artificial abrasive materials or metallurgical slags

Konstantin D. Litasov, Hiroyuki Kagi, Tatyana B. Bekker

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)

Abstract

Recently a number of reports claimed enigmatic appearance of high-pressure and super-reduced minerals in ophiolitic chromitite and peridotite. Diamond, moissanite, various metal alloys, and native metals, carbides and nitrides were found in mineral separates from bulk rock probes of chromitite and peridotite from Tibet, Polar Ural and other localities. Similar findings of super-reduced phases were reported for pyroclastic rocks and alluvial deposits of Mt. Carmel in Israel. We performed the study of microinclusions in corundum grains from abrasive materials produced industrially in an electric arc furnace and found that they are very similar to microinclusions in corundum grains from natural samples. The key similar phases are Ti 3+ 4 Al 2 (Zr,Ti 4+ ) 4 O 11 carmeltazite, Ti 2 O 3 tistarite, TiN 1-x , TiC 1-x , Fe–Si and Fe-Si-Ti alloys, hibonite, grossite, anorthite, and residual feldspatic glass. Although some differences between abrasive corundum and corundum from Tibet and Mt. Carmel are obvious, the morphology of melt pockets and amount of mineralogical similarities is more than critical to suggest that they can be of the same origin. The additional possible source of corundum grains with super-reduced inclusions is various Al-bearing slags after aluminothermic reactions during steelmaking. Moreover, taking into account the spectacular similarity of diamonds from ophiolite with synthetic diamonds, we claim for a thorough reconsideration of ultrahigh-pressure and super-reduced phases in natural rocks and argue that we need to find criteria for discrimination between natural and artificial samples. One of the strongest criteria would be textural and structural features that clearly demonstrate the indigenous character of the host minerals.

Original languageEnglish
Pages (from-to)181-190
Number of pages10
JournalLithos
Volume340-341
DOIs
Publication statusPublished - 1 Sep 2019

Keywords

  • Abrasive
  • Chromitite
  • Corundum
  • Fused alumina
  • High-pressure
  • Ophiolite
  • Peridotite
  • Subduction
  • Super-reduced phases
  • PODIFORM CHROMITITES
  • ULTRAHIGH-PRESSURE
  • CRYSTAL-STRUCTURE
  • LUOBUSA OPHIOLITE
  • DIAMOND-BEARING
  • UPPER-MANTLE
  • ORIGIN
  • METAL-ALLOYS
  • SUTURE ZONE
  • UNUSUAL MINERALS

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