Tranquillityite
| Tranquillityite | |
|---|---|
| General | |
| Category | Silicate mineral (nesosilicate group) |
|
Formula (repeating unit) |
(Fe2+)8Ti3Zr2 Si3O24 |
| Strunz classification | 9.AG.90 |
| Dana classification | 78.07.16.01 (Unclassified silicates) |
| Crystal system |
Hexagonal Unknown space group |
| Unit cell | a = 11.69, c = 22.25 [Å] Z = 6; V = 2,633.24 Å3 |
| Identification | |
| Color | Gray, dark red-brown in transmitted light |
| Crystal habit | Lath shaped grains generally found as inclusions in other minerals or interstitial (<0.1% in weight) |
| Luster | Submetalic |
| Diaphaneity | Opaque to semitransparent |
| Density | 4.7 ± 0.1 g/cm3 |
| Optical properties | Biaxial |
| Refractive index | nα = 2.120 |
| Pleochroism | No |
| 2V angle | 40° |
| Common impurities | Y, Hf, Al, Cr, Nb, Nd, Mn, Ca |
| References | |
Tranquillityite is 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 from which the rock samples in which it was found were brought during the Apollo 11 mission in 1969. Until its discovery in Australia in 2011, it was the last mineral brought from the Moon which was thought to be unique, with no terrestrial counterpart.
In 1970, material scientists found a new unnamed Fe, Ti, Zr- silicate mineral containing rare-earths and Y in lunar rock sample 10047. The first detailed analysis of the mineral was published in 1971 and the name “tranquillityite” was proposed and later accepted by the International Mineralogical Association. It was later found in lunar rock samples from all Apollo missions. Samples were dated by Pb/Pb ion probe techniques.
Together with armalcolite and pyroxferroite, it is one of the three minerals which were first discovered on the Moon, before terrestrial occurrences were found. 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, Western Australia in 2011. The Australian occurrences include a number of Proterozoic to Cambrian age diabase and gabbro dikes and sills. It occurs as interstitial grains with zirconolite, baddeleyite, and apatite associated with late stage intergrowths of quartz and feldspar.
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