Figure 9.

Principal component analysis biplots of APXS of Gale soil targets with oxides contributing to each factor highlighted for (a) principal components 1 and 2 and (b) principal components 3 and 4. Soils in the Rocknest area from Bradbury Rise and High and Namib Dunes are color coded. Gusev and Meridiani average soil compositions are also plotted for comparison. Data were normalized to the mean for each oxide prior to PCA computation. Line length for each factor (the oxide vector transformed into the eigenvector coordinate axes) is proportional to its importance in accounting for the data variance within each principal component. Chemical data included in this PCA were Na₂O, MgO, Al₂O₃, SiO₂, P₂O₅, SO₃, K₂O, CaO, TiO₂, Cr₂O₃, and FeO.