The geochemical analysis of Chione californiensis shells is carried out to study the environmental zonal variation in the Iraqi coasts—north Arabian Gulf. Samples of shells and sea water are collected during low tide period from March to August 2011, from three different stations (Khor Abdullah, Khor Shytianah, and Hacham Island). The studied water samples have clearly indicated that chloride group are the dominant with one major family (Chloride-sodium family) and one water type which is rNa > rMg > rCa; rCl > SO4. The hydrochemical analysis reflects relatively three zones of water salinity namely Khor Abdullah with TDS ranges from 39,215 to 40,100 ppm, Khor Shytianah with TDS ranges from 44,620 to 45,220 ppm and Hacham Island with TDS ranges from 41,190 to 41,220 ppm. X-ray diffractometry of shells of C. californiensis reveals that they have two layers, an inner layer constitutes of aragonite and outer layer constitutes of calcite. The geochemical analyses of the whole shell of C. californiensis reveal positive correlation between water salinity, chemical constituents. Exception is found for SiO2, Al2O3, and P2O5 which have negative correlation with water salinity. The chemical constituents of SiO2 %, Al2O3 %, MgO %, Fe2O3 %, Co, Zn, Cr, and Pb show direct relation with the calcite whereas CaO %, P2O5 %, Na2O %, K2O %, Ba, Sr, Rb, and Sr/Ca ratio show direct relation with the aragonite. The shell of Chione californiensis is found to be a useful tool for monitoring contamination in the Iraqi marine environments.