Chemical composition of Martian fines

Of the 21 samples acquired for the Viking X-ray fluorescence spectrometer, 17 were analyzed to high precision. Compared to typical terrestrial continental soils and lunar mare fines, the Martian fines are lower in Al, higher in Fe, and much higher in S and Cl concentrations. Protected fines at the two lander sites are almost indistinguishable, but concentration of the element S is somewhat higher at Utopia. Duricrust fragments, successfully acquired only at the Chryse site, invariably contained about 50% higher S than fines. No elements correlate positively with S, except Cl and possibly Mg. A sympathetic variation is found among the triad Si, Al, Ca; positive correlation occurs between Ti and Fe. Sample variabilities are as great within a few meters as between lander locations (4500 km apart), implying the existence of a universal Martian regolith component of constant average composition. The nature of the source materials for the regolith fines must be mafic to ultramafic.