Coalescence and microstructure of buried CoSi2 layers formed by 100 keV Co+ implantation at 350°C into Si(111) are studied. Doses ranged from 1×1016 to 1.6×l017 cm−2. The critical dose (dc) required to form a continuous layer is found to be the same, 1.1±0.1×l017 cm−2, in both (111) and (001) substrates, despite pronounced differences in precipitate morphology. Three types of precipitates are observed in Si(111) during the mesotaxial process: A–type (fully aligned), B0–type (twinned on the (111) plane parallel to the surface), and B1,2,3–type (twinned on one of the three (111) planes inclined to the surface). The fraction of each varies with both the implantation and annealing conditions. Formation of a continuous, twinned (B0–type), buried layer after 1000°C annealing is shown to be possible for the first time by this synthesis technique in samples implanted at dc.