Armalcolite

Armalcolite
Armalcolite (Grain size 5 mm)
General
Category	Titanium mineral
Formula (repeating unit)	(Mg,Fe2+)Ti2O5
Strunz classification	4.CB.15
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Bbmm
Unit cell	a = 9.743(30) b = 10.023(20) c = 3.738(30) [Å], Z = 5
Identification
Color	Gray to tan in reflection, opaque
Mohs scale hardness	<5
Luster	Metallic
Specific gravity	4.64 g/cm3 (measured)
Optical properties	Biaxial
References

Armalcolite /ˌɑːrˈmɑːlkəlaɪt/ is a titanium-rich mineral with the chemical formula (Mg,Fe²⁺)Ti₂O₅. It was first found at Tranquility Base on the Moon in 1969 and is named for Armstrong, Aldrin and Collins, the three Apollo 11 astronauts. Together with tranquillityite and pyroxferroite, it is one of three new minerals that were discovered on the Moon. Armalcolite was later identified at various locations on Earth and has been synthesized in the laboratory. The synthesis requires low pressures, high temperatures and rapid quenching from about 1,000 °C to the ambient temperature. Armalcolite breaks down to a mixture of magnesium-rich ilmenite and rutile at temperatures below 1,000 °C, but the conversion slows down with cooling. Because of this quenching requirement, armalcolite is relatively rare and is usually found in association with ilmenite and rutile, among other minerals.

Armalcolite was originally found on the Moon, in the Sea of Tranquility at Tranquility Base, and also in the Taurus–Littrow valley and the Descartes Highlands. The largest amounts were provided by the Apollo 11 and 17 missions. It was later identified on Earth from samples of lamproite dikes and plugs taken in Smoky Butte, Garfield County, Montana, US. On the Earth, it also occurs in Germany (Nördlinger Ries impact crater in Bavaria), Greenland (Disko Island), Mexico (El Toro cinder cone, San Luis Potosí), South Africa (Jagersfontein, Bultfontein and Dutoitspan kimberlite mines), Spain (Albacete Province and Jumilla, Murcia), Ukraine (Pripyat Swell), United States (Knippa quarry, Uvalde County, Texas and Smoky Butte, Jordan, Montana) and Zimbabwe (Mwenezi District). Armalcolite was also detected in lunar meteorites, such as Dhofar 925 and 960 found in Oman.