Abstract
We discuss about precipitation processes of metastable phases from low temperature solution on the basis of observation for their textures and occurrence. Metastable minerals, which precipitate under metastable condition or out of stable region, are major in mineral species on the earth, and contribute to the diversity of minerals. It is considered that origins of the metastable phase were effects of impurity and interface energy. We will propose a new model for nucleation process of the metastable phase.