Mairan is a lunar impact crater that is located on a highland peninsula between Oceanus Procellarum to the west and Mare Imbrium to the east.

It was formed by two volcanic episodes 3.75±0.1 and 3.35±0.2 billion years ago, extruding a viscous silicic lava simultaneously with basalt eruptions in nearby mare.

[2] In the mare, due west of Mairan, is a small lunar dome designated Mairan T with 3.8 km wide depression at the summit (in official IAU nomenclature "Mairan T" name refers only to the depression), believed to be a caldera[3] The width of hill is about 7 km, and height is about 800 m.[4] It is one of four unusually steep (with slopes reaching 22-27 degrees) and bright domes in area which are thought to be formed by very viscous, high-Si lava.

[5] The composition of domes is changing from the north to south, with Mairan Northwest composed of pyroxenes with 30% quartz admixture, while Mairan South dome composed of nearly pure quartz, with extremely high thorium concentration of 83±19 ppm.

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Mairan.