Geological Chronicle
Arzachel is a relatively undegraded lunar impact crater in the south-central highlands of the visible Moon, situated close to the zero meridian. It lies south of Alphonsus and, together with Ptolemaeus further north, forms a prominent crater chain east of Mare Nubium. On the lunar geologic timescale, Arzachel is of Lower (Early) Imbrian age. Although generally circular in shape, evidence suggests it was formed by an oblique impactor arriving from the south. The rim shows little sign of wear, with a rough outer rampart joining a ridge that runs to the southern rim of Alphonsus, while the interior features detailed terrace structures that are especially marked along the slightly higher eastern rim.
Across the interior, a rugged central peak rises 1.5 kilometers above the floor. The peak is somewhat offset to the west and follows a bowed curve from south to north-northeast. Mineralogical rocks in the peak area consist mainly of spinel- and low-calcium pyroxene-bearing material. Spectral signatures of the peak and the inner wall are consistent with anorthositic norite, matching the composition of the crater floor.
The crater floor is relatively flat apart from irregularities in its southwestern quadrant. Arzachel is considered a floor-fractured crater with radial and concentric fractures, though its fractures are not prominent. A rille system named Rimae Arzachel extends from the northern wall to the southeast rim, with higher elevations along its western side than on the east. Prominently situated on the floor east of the central peak is the small crater Arzachel A, accompanied by a nearby pair of smaller craterlets.