Tranquillityite is a silicate mineral with formula (Fe2+)8Ti3Zr2 Si3O24.[ It is mostly composed of iron, oxygen, silicon, zirconium and titanium with smaller fractions of yttrium and calcium. It is named after the Mare Tranquillitatis (Sea of Tranquility), the place on the Moon where the rock samples were found during the 1969 Apollo 11 mission. It was the last mineral brought from the Moon which was thought to be unique, with no counterpart on Earth, until it was discovered in Australia in 2011.]
Discovery
In 1970, material scientists found a new unnamed Fe, Ti, Zr- silicate mineral containing rare-earths and Y in lunar rock sample 10047.[ Samples were dated by Pb/Pb ion probe techniques.][
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Together with armalcolite and pyroxferroite, it is one of the three minerals which were first discovered on the Moon, before terrestrial occurrences were found.[ Lunar Sample Mineralogy, NASA] Fragments of tranquillityite were later found in Northwest Africa, in the NWA 856 Martian meteorite.
Terrestrial occurrences of tranquillityite have been found in six localities in the Pilbara region of Western Australia, in 2011.[
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Properties
Tranquillityite forms thin stripes up to 15 by 65 micrometres in size in basaltic rocks, where it was produced at a late crystallization stage. It is associated with troilite, pyroxferroite, cristobalite and alkali feldspar. The mineral is nearly opaque and appears dark red-brown in thin crystals.[ The analyzed samples contain less than 10% impurities (Y, Al, Mn, Cr, Nb and other rare-earth element) and up to 0.01% (100 ppm) of uranium.]
Irradiation by generated by uranium decay is believed to be the origin of the predominantly amorphous metamict structure of tranquillityite. Its crystals were obtained by annealing the samples at for 30 minutes. Longer annealing did not improve the crystalline quality, and annealing at higher temperatures resulted in spontaneous fracture of samples.
The crystals were initially found to have a hexagonal crystal structure with the lattice parameters, a = 1.169 nm, c = 2.225 nm and three formula units per unit cell,[ but later reassigned a face-centered cubic structure (fluorite-like).][
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See also
- Citations
- Bibliography
External links
