Type B 2 and the core material of type B 1 were formed from materials derived from a supernova and/or from interstellar dusts disseminated by supernovae. They were driven into the prato-solar nebula, and the core material of type B 1 reacted with the nebular gas at high-temperature, forming type B 1 which is surrounded by a melilite mantle. Compact type A was produced by the complete reaction between the high-temperature nebular gas and the core material of type B 1. Fluffy type A was formed by the above-stated complete reaction at temperatures higher than the case of compact type A and/or by aggregation of high-temperature solid condensates in the proto-solar nebula.