Coeval crystallographic growth sectors were microsampled from a fractu
re-filling calcite cement crystal with well-developed crystal faces an
d concentric zoning to test empirically for isotopic sector zoning. Is
otopic and minor element homogeneity among coeval parts of the {01 (1)
over bar 2} and {21 (3) over bar 1} sectors suggests that isotopic se
ctor zoning ages not occur in calcite. Empirical results are compatibl
e with theoretical considerations based on crystal surface geometry, g
rowth mechanisms, and a thermodynamic growth model.