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.