Armalcolite is a mineral that was discovered at Tranquility Base on the Moon by the Apollo 11 crew in 1970. It was named for Armstrong, Aldrin and Collins, the three Apollo 11 astronauts. Examples of this mineral were later discovered in various locations on Earth as well, such as Smoky Butte, Garfield County, USA in lamproite dykes and plugs, Disko Island (Greenland) in native iron, Pripyat Swell (around the Pripyat River, Ukraine) in trachybasalt and in South African kimberlites.

It has a chemical formula of (Mg,Fe⁺⁺)Ti₂O₅, a hardness of 6, and an orthorhombic crystal system. Armalcolite is a part of the pseudobrookite group which consists of minerals of the general formula X₂YO₅. X and Y are usually Fe (2+ and 3+), Mg, Al, and Ti. End members are armalcolite (MgFeTi₂O₅), pseudobrookite (Fe₂TiO₅), and ferropseudobrookite (FeTi₂O₅).