Seeded batch experiments were conducted at low magma densities and moderate ionic strength to determine the growth and aggregation rate constants for calcite precipitation in a stirred vessel The growth was found to be surface-reaction-limited and the growth rates agreed broadly with other studies of calcite precipitation Aggregation rates have rarely been presented for calcite. The aggregation rate constant studied here was directly proportional to the instantaneous growth rate and inversely proportional to the average shear rate ill the vessel The results were also compared with similar work carried out on calcium oxalate monohydrate. It was found that the relationship between the aggregation rate constant and stirrer speed was virtually identical in the two cases, despite almost an order of magnitude difference in the growth rate constants.