Condensation of glass with multimetal nanoparticles: Implications for the formation process of gems grains

Interplanetary dust particles contain grains of glass with embedded metals and sulfides (GEMS; i.e., amorphous silicate grains with diameters of a few hundred nanometers containing Fe nanoinclusions and Fe sulfide particles), which are considered to be among the building blocks of the solar system. To explore that GEMS grains formed during the condensation process, condensation experiments were carried out in Si-Mg-Fe-Al-Ca-Ni-O and Mg-Si-Fe-Ca-Al-Na-O systems using an induction thermal plasma furnace. In all experimental runs, spherical grains (mostly composed of amorphous silicate) with diameter <100 nm formed. The analysis of the amorphous silicates, which were classified as Mg rich or Si rich, indicated that the condensates formed via melting. Fe led to the formation of fine magnetite grains in most of the oxidative experiments, to 10 nm metal grains (i.e., kamacite and taenite) under intermediate redox conditions, and to 30-100 nm Fe silicide grains (i.e., gupeiite, xifengite, and fersilicite) in most of the reductive experiments. Under intermediate redox conditions, some amorphous silicate particles showed multiple Fe inclusions with textures very similar to those of GEMS grains except for FeS, indicating that GEMS could form via melt condensation of high-Temperature gases. Considering the nucleation and growth of solids from high-Temperature gas during cooling, we infer that GEMS grains form either in the local environment of a protosolar disk (and be related to chondrule formations) or around evolved stars related to Type II-P supernovae and asymptotic giant branch-Type stars.