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armalcolite
Armalcolite 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.〔(Lunar Sample Mineralogy ), NASA〕 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.
==Occurrence==
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, USA. 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.〔(Lunar Meteorites: Dhofar 925, 960, & 961 (paired stones) ), Department of Earth and Planetary Sciences, Washington University〕
Armalcolite is a minor mineral found in titanium-rich basalt rocks, volcanic lava and sometimes granite pegmatite, ultramafic rocks, lamproites and kimberlites. It is associated with various mixed iron-titanium oxides, graphite, analcime, diopside, ilmenite, phlogopite and rutile. It forms elongated crystals up to about 0.1–0.3 mm in length embedded in a basalt matrix.〔 Petrographic analysis suggests that armalcolite is typically formed at low pressures and high temperatures.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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