In this experiment, students are given a fanciful application of the standard addition method to evaluate the approximate quantity of the shell component in a sample of sand collected on the Lido di Venezia seashore. Several diffuse reflectance infrared Fourier transform (DRIFT) spectra are recorded from a sand sample before and after addition of known amounts of powdered shell. A peak, characteristic of shells, is selected and its normalized intensity is plotted against the percentage of added shell powder. By means of a linear regression, the initial concentration of the component from shells of the sand is estimated. The proposed approach, based on a method for mixtures and impurity determination, requires students to perform DRIFT spectroscopic measurements of a powdery material and, depending on the starting material, offers the chance to verify the influence of grain size on spectral features. Well-known distortion effects on peak intensities and line shapes due to sample inhomogeneities that usually make DRIFTS a poor technique for quantitative measurements are circumvented by asking students to follow a strict procedure for sample preparation. The proposed experiment can be carried out in one or two lab periods depending whether students are asked to prepare starting powders or determine the optical response curve and is designed for either undergraduate or graduate students. (Contains 3 tables and 9 figures.)