Using Girifalco's potential for describing the interaction between fullerene molecules, we performed molecular dynamics simulations to obtain the ground-state structures of (C-70)(n-x)(C-60)(x) clusters (11 less than or equal to n less than or equal to 22; 0 less than or equal to x less than or equal to n - 1). For all values of x, (C-70)(13-x)(C-60)(x) clusters have a closed-shell icosahedral structure that is more stable than those of neighboring (C-70)(n-x)(C-60)(x) clusters; and for 2 less than or equal to x less than or equal to 10, (C-70)(19-x)(C-60)(x) clusters have a double icosahedral structure that exhibits similarly enhanced relative stability for 2 less than or equal to x less than or equal to 9. The discrepancy between this latter result and experimental findings for ionized fullerene clusters, which suggest that [(C-70)(19-x)(C-60)(x)](+) is more stable than the homologous 18- and 20-member clusters for all x, is tentatively attributed to the ionization-induced alteration of the intermolecular potential.