The alteration layers of the marble statues of Fonte Gaia were analyzed. The characterization of the main components was made by x-ray diffraction (XRD), infrared (IR), colorimetric tests, and stratigraphy. Both mono-and di-hydrate calcium oxalates, together with gypsum, nitrates, silicates, and carbon particles, were detected. The relative amount of oxalates was calculated, giving evidence of a very high extent of weddellite.