Map of the concentration of iron in the units of the Orientale Basin using the methods of Lucey et al. (1995). The vast bulk of Orientale Basin ejecta deposits are very low in iron, between 2 and 6 wt%. Note the multitude of small, black areas within the basin outlining the Inner Rook mountain ring of the basin. These areas have ferrous oxide content below 2 wt%, consistent with a composition of nearly pure anorthosite, a finding confirmed by Earth-based spectrophotometry of several peaks in this ring. The central Mare Orientale shows iron content comparable to several other maria. Note the circular deposit of high-iron material at left center; this high-iron zone corresponds to a low-albedo unit that is probably a deposit of pyroclastic ash.