• DOI:10.2138/am-2003-11-1223
• Corpus ID: 128600868

Letters. Rock-forming moissanite (natural α-silicon carbide)

@article{DiPierro2003LettersRM,
  title={Letters. Rock-forming moissanite (natural $\alpha$-silicon carbide)},
  author={Simonpietro Di Pierro and Edwin Gnos and Bernard Henry Grob{\'e}ty and Thomas Armbruster and Stefano Michele Bernasconi and Peter Ulmer},
  journal={American Mineralogist},
  year={2003},
  volume={88},
  pages={1817 - 1821}
}

• S. Di Pierro, E. Gnos, +3 authors P. Ulmer
• Published 1 November 2003
• Geology
• American Mineralogist

Abstract We report the first occurrence of moissanite (SiC) as a rock-forming mineral (8.4 vol%) in one unique specimen of a terrestrial rock. The sample has a homogeneous, porphyritic texture, and was found as a beach pebble thought to be derived from a Tertiary volcanic province of the Aegean Sea region. The matrix is bluish-colored and consists of very fine-grained brucite, calcite, and magnesite, in which macrocrysts of quartz (25.3 vol%) and moissanite are found. Other accessory phases are phlogopite-3T, magnesiochromite, an Fe-rich phase, Cl-bearing brucite, Al-rich orthopyroxene, and unidentified MgFe-silicates (4 vol%). The bulk-rock composition shows a “kimberlitic” chemistry (55.8 wt% SiO2, 28.5 wt% MgO, 1.4 wt% CaO, 18.1 wt% LOI). Colorless gemmy, and blue or black moissanite crystals are subhedral and display characteristic hexagonal symmetry (6H polytype). Most moissanite grains contain metallic Si and Fe-silicide (Fe3Si7) inclusions, and more rarely, other Fe-silicides with varying amounts of Al (≤24.5 wt%), Ca (≤8.0 wt%), Mn (≤6.8 wt%), Ti (≤16.3 wt%), and Ni (≤2.6 wt%). The δ13C value of the moissanite is -28.1‰. According to available data, the fO2 stability field of SiC is five to six log units below the iron-wüstite (IW) buffer curve. Therefore, the observed Fe-bearing silicates cannot have been equilibrated with SiC under ambient pressure. Instead, our finding indicates that the rock most likely formed at the ultrahigh-pressure conditions of the upper mantle or transition zone.