International team including UMaine research professor Edward Grew reports two new nanominerals from Tibet

Edward Grew, research professor in the School of Earth and Climate Sciences at the University of Maine, has assisted an international team with obtaining approval for two new nanominerals from a mine in Tibet.

In 2018, Grew was invited to join the research team led by Fahui Xiong and including Xiangzhen Xu, Paul T. Robinson, and Jingsui Yang from Beijing, Guangzhou and Nanjing in China; Enrico Mugnaioli and Mauro Gemmi from the Center for Nanotechnology of the Istituto Italiano di Tecnologia in Pisa, Italy; and Richard Wirth from the Helmholtz Center in Potsdam, Germany.

Grew helped to develop and guide the proposals for the new minerals through the rigorous review and approval by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA). He also co-authored the journal article reporting the discoveries, published Nov. 2, 2020 in the European Journal of Mineralogy: “Two new minerals, badengzhuite, TiP, and zhiqinite, TiSi2, from the Cr-11 chromitite orebody, Luobusa ophiolite, Tibet, China: is this evidence for super-reduced mantle-derived fluids?

In recent years, new technology has made it possible to investigate and characterize very tiny crystals of minerals. Increasingly, new minerals approved by IMA are so small that they can only be seen with an electron microscope. The new minerals studied by Grew were found as inclusions in crystals of corundum extracted from chromitite ore from a mine in the Luobusa ophiolite in southern Tibet.

Ophiolites are slices of ocean crust and upper mantle that are incorporated in mountain belts when continents collide as a result of tectonic plate motion. One of the great ophiolite belts of the world is in Tibet, where the Indian subcontinent collided with the rest of Asia and pushed up the Himalaya Range. The surface expression of this boundary is the Yarlung-Zangbo Suture Zone south of Lhasa, Tibet, along which a series of ophiolites hosts the largest economic chromite deposits in China. The new minerals are interpreted to have formed in the Earth’s upper mantle by the action of mantle methane and hydrogen on basaltic melts in the Luobusa ophiolites.

The new minerals, named after Chinese geologists, have simple chemical formulas: badengzhuite TiP (titanium monophosphide) and zhiqinite, TiS2 (titanium disilicide).  Both compositions and structures have been previously synthesized in the laboratory, but this is their first reported occurrence in a geologic setting. The nanominerals were characterized by 3D electron diffraction, which can solve the crystal structures of phases less than a micrometer in size.|

The results of this research contribute to our understanding of the mineralogy of ophiolites and deeply subducted crustal rocks and their exhumation back to the Earth’s surface. The remarkable complexity of the assemblage of nanominerals also demonstrates the fractal nature of mineral assemblages.