Abstract An approach is presented to obtain a truly rational interpretation of the Martian surface and atmosphere. Polarimetric and photometric properties of ore specimens (limonite, siderite, desert varnish, and serpentine), considered good prospects for the Martian surface, are presented for the colors B(0.48 μ), G(0.54 μ), and I(1.0 μ). This data was obtained with a large-scale analyzer. Other measurements to better define the specimens are also described. It is concluded that, assuming a small atmospheric influence, the best optical match to the Martian bright areas occurs with Venango County, Pennsylvania limonite, with a dominant particle size range between 1 and 2 mm, and a subsidiary minor distribution of a smaller particle size. The smaller particles are suggested as