Three-dimensional observation of GEMS grains: Their high-temperature condensation origin

Geochimica et Cosmochimica Acta (in Press) Link to Article []
1Research Organization of Science and Technology, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga, 525-7, Japan
2CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (CAS), Guangzhou 510640, China
3CAS Center for Excellence in Deep Earth Science, Guangzhou 510640, China
4Division of Earth and Planetary Sciences, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo, Kyoto 606-8502, Japan
5Johnson Space Center, NASA, Houston, TX 77058, United States
6Present address: Blue 22 Software, Houston, TX
Copyright Elsevier

GEMS (Glass with Embedded Metal and Sulfides) grains found in interplanetary dust particles are considered one of the most primitive materials in the Solar System, yet questions remain on how they formed. It has been suggested that GEMS grains are products of radiation processing and amorphization of sulfide and silicate mineral grains in the interstellar medium. Alternatively, GEMS grains are proposed to be disequilibrium condensation products in late-stage protosolar disks. We examined the 3D distributions of elements and inclusions within GEMS grains using TEM (transmission electron microscopic)-tomography to better constrain their possible formation processes. We found some core-shell particles composed of metals and amorphous silicates and observed a binary distribution of Mg/Si in amorphous silicates of GEMS grains. These properties are highly similar to the features of experimental condensation products. Furthermore, the location of sulfides only on the surface of GEMS and their larger sizes than metals are also consistent with the condensation experiments, where sulfides formed by sulfidation of metal grains with S-bearing gas species. Textures showing aggregation and possible coalescence of primary grains were also observed. Therefore, we conclude that GEMS grains are condensates from gas at high temperatures and some of them were aggregated.


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