Geological Chronicle
Mons Hansteen, also designated Hansteen Alpha (α), is a roughly triangular mountain on the western margin of Oceanus Procellarum, situated southeast of Hansteen crater and north of Billy crater. Covering a base diameter of 30.65 kilometers, the structure belongs to a rare class of non-mare lunar volcanoes. The formation is thought to be a volcanic extrusion younger than Hansteen crater, with surface volcanic ash deposited between 3.5 and 3.74 billion years ago.
The extruded material of Mons Hansteen is significantly enriched in silica and strongly depleted in iron and titanium oxides compared to surrounding mare terrain. Initially, it was believed its lavas were not as evolved as those of the Compton–Belkovich Thorium Anomaly, but by 2004 the low thorium enrichment signal was attributed to the small size of the volcanic complex, establishing a composition compatible with highly processed silicic lavas.
By 2013, patchy deposits of magnesium spinel were detected in the central and western parts of the volcanic dome. These spinel-rich areas are associated with boulder fields and fringed by areas showing signs of hydration, where 4 to 8 percent of mineral by weight is hydroxylated. The average bulk density of material in Mons Hansteen is extremely low, measuring between 1,500 and 2,000 kg/m³.