The effects of growth kinetics, temperature and solution composition on Mn 2+ and Fe 2+ incorporation into calcite were investigated. Mn- or Fe-bearing overgrowths on calcite seeds were precipitated at 10°, 25° and 50°C from solutions with various metal Ca 2+ molar ratios over a range of precipitation rates using a “chemo-stat” technique. Homogeneous distribution coefficients for Fe 2+ ( D Fe 2+ ) and Mn 2+ ( D Mn 2+ ) incorporation increase with decreasing precipitation rate or increasing temperature. Although previous work suggested a decrease in D Mn 2+ with increasing temperature, this likely is attributable to concurrent increases in precipitation rate. At the temperatures investigated, D Mn 2+ is greater than D Fe 2+ and the ratio D Mn 2+ D Fe 2+ increases with decreasing precipitation rate. D Mn 2+ varied from 3.8 to 16 over a range of precipitation rates of 450 to 45,000 μmol m −2 hr. −1 at 25°C. Mn-calcite compositions ranged from 0.5 to 40 mol% MnCO 3 over all of the solution Mn 2+ Ca 2+ ratios investigated and a small decrease (∼20%) in D Mn 2+ was observed in solutions with the highest Mn 2+ Ca 2+ ratio. The dependence of D Mn 2+ on precipitation rate was unaffected by an order of magnitude change in P CO 2 , but a small difference was observed with an order of magnitude change in CaCl 2 concentration. D Mn 2+ varied from 3 to 11 at 10°C and from 8 to 22 at 50°C over a similar range of precipitation rates. D Fe 2+ varied from 1.9 to 3.7 for precipitation rates from 800 to 50,000 μmol m −2 hr. −1 at 25°C and the Fe-calcites contained <0.4 mol% FeCO 3. D Fe 2+ exhibited a more pronounced, but still relatively small, decrease with increasing Fe 2+ concentration. D Fe 2+ varied from 1.5 to 2.3 at 10°C and from 2.8 to 7.7 at 50°C. Application of these results to the interpretation of Fe and Mn content in diagenetic calcites is discussed. Effects of precipitation rate and temperature on D Mn 2+ and D Fe 2+ could produce compositional variations in calcite cements causing cathodoluminescent zoning, but are unlikely to be responsible for the major variations commonly observed in natural cements.