Tranquillityite
A rare iron–zirconium–titanium silicate first found in Apollo 11 Moon rocks.
Key facts
- Formula
- Fe8(Zr,Y)2Ti3Si3O24
- Family
- Silicates
- Crystal system
- Hexagonal
- First described
- Apollo 11 basalts from the Sea of Tranquillity, 1971
Tranquillityite was described in 1971 from basalts collected by Apollo 11 in the Sea of Tranquillity. For four decades it was known only from the Moon, until it was identified in 2011 in rocks from several sites in Western Australia.
What it is
Tranquillityite is a silicate rich in iron, titanium and zirconium, with yttrium. It crystallises in the very last pockets of melt in a basalt, where elements that do not fit into common minerals become concentrated.
Where it is found
It is found in lunar mare basalts and some lunar meteorites, always as tiny laths with other late-stage minerals. Because it holds uranium, it has been used to date lunar basalts and, on Earth, Australian dolerites.
How it is recognised
It forms thin reddish-brown laths, usually less than 0.1 mm long, seen in polished sections and identified by chemistry.
Did you know?
For 40 years tranquillityite was thought to be found only on the Moon.
Its Australian occurrence was recognised by comparing old museum thin sections with lunar descriptions.