Discovery of terrestrial rubinite, Ca3Ti3+2Si3O12, super-reduced garnet from the Hatrurim Complex, Israel

Evgeny V. Galuskin, Irina O. Galuskina, Joachim Kusz, Yevgeny Vapnik, Grzegorz Zieliński

Research output: Contribution to journalArticlepeer-review

Abstract

Rubinite, a garnet with the ideal formula Ca3Ti3+2Si3O12, is an indicator of super-reduced conditions and has recently been found in refractory inclusions in a few CV3 chondrites. We discovered rubinite in phosphide-bearing breccia from the pyrometamorphic Hatrurim Complex, Negev Desert, Israel. Aggregates of phosphide and native iron are concentrated at the boundary of thermally altered sedimentary xenoliths encased in flamite-gehlenite paralava. Rubinite, with the average empirical formula (Ca2.97Mg0.02Fe2+0.01)∑3.00 (Ti3+1.10 Al0.44Ti4+0.37Mg0.08Cr0.01)∑2(Si2.71Al0.29)∑3.00O12, was found in a small xenolith composed of hydrogrossular, tacharanite and calcite, and containing relics of high-temperature minerals such as pseudowollastonite, cuspidine, gehlenite, baghdadite, barringerite, murashkoite, osbornite, paqueite and oldhamite. For the first time, a structure of rubinite, with the composition (Ca2.99Mg0.01)∑3(Ti3+0.78Al0.62 Ti4+0.43Mg0.17)∑2(Si2.74 Al0.26)∑3O12, has been refined. Its unit-cell parameter a = 12.0193(4)Å, is significantly smaller than that of the synthetic analogue of Ca3Ti2Si3O12, 12.1875Å. In a Raman spectrum of rubinite weak bands corresponding to the vibrations of Ti4+-O in the (TiO6)8- octahedra: 610 cm-1 ν1(TiO6)8- and 438 cm-1 ν4(TiO6)8- are present in addition to the bands related to Si-O and Al-O vibrations in the TO4 tetrahedra. Rubinite forms a thin reactive rim (<10 μm) on pseudowollastonite grains. It likely formed during a sharp increase in rock porosity in the course of natural clinkerisation of sedimentary xenoliths caused by the thermal impact of the paralava. The high porosity increased the effect of reductive gases on the rocks, which were by-products of pyrometamorphism. The brief appearance of super-reduced conditions defined the formation of the Ti3+-bearing minerals osbornite and rubinite.

Original languageEnglish
JournalMineralogical Magazine
DOIs
StateAccepted/In press - 1 Jan 2025

Keywords

  • garnet
  • Hatrurim Complex
  • Israel
  • paralava
  • Raman
  • rubinite
  • structure
  • super-reduced minerals
  • terrestrial rock

ASJC Scopus subject areas

  • Geochemistry and Petrology

Fingerprint

Dive into the research topics of 'Discovery of terrestrial rubinite, Ca3Ti3+2Si3O12, super-reduced garnet from the Hatrurim Complex, Israel'. Together they form a unique fingerprint.

Cite this