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Armalcolite (/ˌɑːrˈmɑːlkəlt/) is a titanium-rich mineral with the chemical formula (Mg,Fe2+)Ti2O5. It was first found at Tranquility Base on the Moon in 1969 during the Apollo 11 mission, 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.[5] Armalcolite was later identified at various locations on Earth and has been synthesized in the laboratory. (Tranquillityite and pyroxferroite were also later found at various locations on Earth).[6] 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.

Quick facts: Armalcolite, General, Category, Formula .mw-p...
Armalcolite from Myanmar (grain size 5 mm)
CategoryTitanium mineral
(repeating unit)
IMA symbolArm[1]
Strunz classification4.CB.15
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupBbmm
Unit cella = 9.743(30)
b = 10.023(20)
c = 3.738(30) [Å], Z = 5
ColorGray to tan in reflection, opaque
Mohs scale hardness<5
Specific gravity4.64 g/cm3 (measured)
Optical propertiesBiaxial