Observations have confirmed the formation of dust grains in the metal-rich ejecta of SN 1987A. In this paper the grain formation in the ejecta is reinvestigated on the basis of the revised hydrodynamical model and elemental composition of the ejecta, and of the theory of homogeneous nucleation and grain growth. The adopted abundance distribution in the ejecta, inferred from the behavior of the bolo metric light curve around its maximum and the early emergence of X-rays and)I-rays, results in the sequential formation of Alz0 3 , MgSi03 and Fe30 4 grains respectively in the ejecta at 1.0 M 0 :S; Mr :s;4.4 M0 as the gas cools down. In the inner region at Mr:S; 1.0 M 0 , on the other hand, the latent heat deposited during the grain growth retards the formation of dust grains. The observed enhancement of 10 Ilm flux at-day 465 after the explosion being assigned to the thermal radiation from Al z 0 3 grains formed in the ejecta, MgSi0 3 grains start to form at-day 550, and Fe30 4 grains at-day 620, and the grains cease to form at-day 730 in the region at 1.0 M 0 :s; Mr:S; 4.4 M 0' The total mass of dust grains formed in this region is-0.23 M 0' The radii of grains newly formed in the ejecta are typically-10 A for Al z 0 3 and Fe 3 0 4 , and-70 A for MgSi0 3 grains. The calculated grain radius smaller than 0.01 Ilm satisfies the constraint on the grain size in the ejecta imposed by the analysis of the blue-shifted optical lines. Comparing the observed infrared light curve with the calculated one based on both the condensation calculation and the observed 10 Ilm flux, we suggest that: 1) The condensation efficiency of dust grains in the ejecta is greater than 0.3, or the clumps occupies the fraction of at least-20% of the ejecta on the average. 2) The grain number density in the clumps is less than 5 times that of the uniform ejecta. 3) The observed infrared luminosity is attributed to the thermal radiation from dust grains in the optically thick part of the ejecta.

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General picture of grain formation is preoented based on the nucleation theory. Grain formation process is described by a growth equation of grain radius and an equation of monomer consumption due to the growth of grains. These equations are characterized by two parameters. One depends on the physical conditions of the system and the other reflects the nature of grain materials. An overall feature of the grain formation process is illustrated by the use of an analytic expression of the solutions. After the vapor cools down to the saturated state, a waiting time is necessary until the grain formation begins effectively. Size distribution is relatively sharp in general. The representative size is closely related to the parameter which depends on the physical conditions. Growth by coalescence is not effective until the monomer sticking process is almost completed. The results are applied to the condensation in the primordial solar nebula. It is shown how the picture based on the chemical equilibrium calculations should be modified.

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