2002 年 31 巻 1 号 p. 46-49
Silica minerals are poorly encountered in meteorites and the terrestrial planets. Especially, primitive meteorites, except enstatite chondrites, rarely contain silica minerals. This mainly reflects the solar elemental abundance that Mg is more abundant than Si. Unless the extensive magmatic fractionation took place for long time, silica minerals did not become common minerals in the planets. In spite of their rare occurrences, the polymorphs of silica minerals are significant to estimate the physical conditions of the formation processes of meteorites and planetary rocks.