Ultrafine barium titanate particles in the Allende meteorite

Abstract

Many small particles of barium titanate were discovered in the Allende meteorite. Although the particles are distributed heterogeneously in the meteorite, their presence in matrix is not unusual for Allende. Two types of concentration pattern are observed. One is skeleton-type. Barium titanate particles are distributed in very small inclusions of the meteorite, as if the particles construct a skeleton of the inclusion. Another distribution pattern is spot-type. Aggregates of barium titanate particles are distributed in fine-grained matrix of the meteorite and show no bearing on their surroundings. REE abundances are determined for two skeleton-type barium-titanate rich parts with accompanied high-temperature minerals. Their chondrite-normalized REE patterns have V shape as expected by TANAKA et al. (1976). Based on the data obtained by EPMA, BaO and TiO2 contents turn out to be 59 and 34%, respectively. Any relation with Ca and Sr which form the other titanates could not be detected in the present investigation. According to the calculation, fundamental barium titanate particulate seems to have the maximum radius of 0.2μm. Observed Ba and Ti contents are explained by the dimensions of X-ray production being wider than the area of aggregate of the fundamental barium titanate particulate. The particles seem to have existed prior to the early condensation stage of high-temperature minerals and some particles played a role of skeleton of small high-temperature minerals. Other particles exempted from such roles, gathered together and formed a large (∼1μm) spot-type Ba-rich cluster. The ultrafine barium titanate particles seem to suggest the particles being free from an early vaporization episode of the nebula.