[1] This mare differs from most of the nearside maria; it has an irregular outline and it appears to be fairly thin.

It has small circular and elongated features in the mare plains that probably mark impact craters buried by less than 1000 to 1700 feet (300 to 500 m) of lava.

The major crater to the north of Marginis is Al-Biruni, with Ibn Yunus to the southeast and Goddard to the northwest.

The surface of this mare displays some lunar swirls; higher albedo deposits that are similar to the Reiner Gamma feature on the Oceanus Procellarum.

Other possible explanations for the formation include a cometary impact, venting of volcanic gases, or just normal surface markings that are shielded from space weathering due to the magnetic field.