A large beachfront resort recently installed expensive white marble floor tiles in several of their units as part of a renovation. Over time, large reddish stains began to appear on many of the white tiles especially those in high foot traffic areas. The custodial services at the resort were not able to remove the stains and thus contacted EMSL for the cause and solution to this problem. Upon through examination of the tiles with and without the reddish stain, polarized light microscopy and electron microscopy revealed the presence of fine crystals of pyrite present only in the tiles with the reddish stains. EMSL surmised that as the guests of the resort tracked in seawater, the salts reacted with the iron in the pyrite and thus produced the reddish color. EMSL not only showed the resort how to avoid this problem, but also showed the tile manufacturer how to screen their tiles for this.