The Ksp represents the concentrations that result if the water is in equilibrium with the
solid. If the IAP is less than the Ksp, the mineral should dissolve. If the IAP is greater
than the Ksp, then the concentrations must decrease via mineral precipitation. In the
present case, the IAP (10-7) > Ksp (10-8.3) and so calcite can, indeed, precipitate.