Synchronous intracrystalline delta C-13 and delta O-18 differences in natural calcite crystals

New intersectorial isotope data are presented for two calcites. Mendip calcite shows no detectable delta(13)C and delta(18)O differences between synchronous {21 (3) over bar 4} and {01 (1) over bar 4} sectors. Nottingham calcite shows a delta(13)C difference of 1.0 parts per thousand and a delta(18)O difference of 0.5 parts per thousand between synchronous {40 (4) over bar 1} and {0001} sectors. Data now available for 5 different calcites show the magnitude of intersectorial fractionation is variable; the effect on delta(13)C is twice that on delta(18)O. All five natural calcites also show erratic isotopic differences between symmetrically-equivalent synchronous sectors. Intersectorial isotopic fractionation is probably widespread but its cause and quantification require further work. Synchronous intracrystalline isotopic differences should be accommodated in the interpretation of isotopic data and should influence future sampling strategy.