New Mineral: Machiite

A new ultra-refractory mineral discovered in the Murchison meteorite [Data link from the Meteoritical Database] has been named after Dr. Chi Ma, the Director of the Geological and Planetary Sciences Division–Analytical Facility at Caltech. He is distinguished for his nano-scale mineralogical expertise and discoveries of many new minerals.

Backscattered electron image of a portion of the Murchison meteorite showing new mineral, machiite, intergrown with corundum. The oval spot in each crystal is a region sputtered during oxygen-isotope measurement. Image courtesy of Alexander Krot, University of Hawai‘i. (From Makide, K. et al., 2013, Geochim. Cosmochim. Acta, v. 110, p. 190-215, figure 9d.)

The mineral and name, machiite, were approved in October, 2016 by the International Mineralogical Association's Commission on New Minerals, Nomenclature, and Classification.

Machiite, Al₂Ti₃O₉, was discovered by cosmochemist Alexander N. Krot (University of Hawai‘i). The mineral has a general formula of (Al,Sc)₂(Ti,Zr)₃O₉ and is the aluminum analogue of the vanadium, titanium oxide mineral schreyerite. Machiite was found intergrown with corundum in the matrix of Murchison and was discovered to be ¹⁶O-poor compared to corundum (Δ¹⁷O values of 0‰ and -24‰, respectively).

Similar to refractory solids previously identified in meteorites, machiite could have either condensed from solar nebula gas or crystallized from a refractory melt before the planets formed, about 4.6 billion years ago. Oxygen isotope disequilibrium between machiite and corundum may indicate post-crystallization oxygen-isotope exchange in the protoplanetary disk. Studies of these early solids are invaluable for understanding the details of nebular evolution and the formation of asteroids and planets.

 (pdf version)

See References:
·   Krot, A. N. (2016) Machiite, IMA 2016-067. CNMNC Newsletter No. 34, December 2016, page 1317; Mineralogical Magazine, v. 80, p. 1315-1321, doi: 10.1180/minmag.2016.080.086. [ link, may require login ]
·   Makide, K., Nagashima, K., Krot, A. N., Huss, G. R., Hutcheon, I. D., Hellebrand, E., and Petaev, M. I. (2013) Heterogeneous Distribution of ²⁶Al at the Birth of the Solar System: Evidence from Corundum-bearing Refractory Inclusions in Carbonaceous Chondrites, Geochimica et Cosmochimica Acta, v. 110, p. 190-215, doi: 10.1016/j.gca.2013.01.028. [ abstract ]

See also:
·   Dr. Chi Ma's new mineral announcements.

Written by Linda Martel, Hawai‘i Institute of Geophysics and Planetology, for PSRD.