Abstract
Under a levitated environment, it is predicted that the crystallization of totally melted droplets would be difficult, because of the requirement of the nucleation process. Therefore, nucleation rate of chondrule melts is also thought to be difficult. We investigate the nucleation rate of Mg-silicate, which is main component of the chondrules, by using a gas-jet levitator.Starting materials are spherules (= 2-3 mm). We prepared pellets of powdered reagents of MgO and SiO2 mixed with MgO/SiO2 mol of 1.0 (enstatite)-2.0 (forsterite). The gas-jet levitator (Nagashima et al., 2006) consists of an aluminum diffuser and an inlet for the argon gas jet (10 m/s).During the cooling process, the forsterite melt set on the graphite rod did crystallize at very small supercooling (dT = 50 K). In contrast, the levitated forsterite melt also showed crystallization, but at larger supercooling (dT > 1000 K). And spontaneous crystallization from levitated chondrule melts is very difficult and the "almost chondrules" should turn into glass in spite of the slow cooling. Therefore, the crystallization of chondrules might occur by collisions with cosmic dusts.
