Aragonite crystal orientation in mollusk shell nacre may depend on temperature. The angle spread of crystalline aragonite tablets records the water temperature at which nacre was deposited by Pinctada margaritifera

Nacre{,} or mother-of-pearl{,} is a lamellar composite of aragonite (CaCO3) tablets with a broad distribution of angular orientations. The angle spread is the full-width of this distribution. Here we analysed the angle spread as a function of position in the nacre layer of one Pinctada margaritifera shell{,} compared the results with temperature data{,} and found these two parameters to be highly correlated. This result suggests that one could calculate the temperature at which nacre formed by measuring only its angle spread. Validation of the correlation in modern and ancient nacre from other species is necessary{,} but if confirmed{,} nacre could provide a physical proxy for temperature in modern and ancient climates.