Merrillite
The main phosphate mineral of most meteorites and of lunar and Martian rocks.
Key facts
- Formula
- Ca9NaMg(PO4)7
- Family
- Phosphates
- Crystal system
- Trigonal
- First described
- stony meteorites (named 1917)
Merrillite was named in 1917 after George Merrill, a curator at the Smithsonian Institution who had identified this calcium phosphate in stony meteorites. It has since been found on Earth only in tiny amounts.
What it is
Merrillite is a calcium phosphate with sodium and magnesium. It resembles the Earth mineral whitlockite, and the two names were long used interchangeably, but merrillite contains no hydrogen. The lack of hydrogen reflects the dry conditions in which most meteorites formed.
It concentrates the rare earth elements and uranium, making it useful for dating.
Where it is found
It occurs as small grains in ordinary chondrites, often next to metal and troilite, and in eucrites, mesosiderites, pallasites, lunar basalts and Martian meteorites. In shergottites it holds most of the rock's rare earth elements.
How it is recognised
It is colourless and is found with an electron microprobe or by its glow under an electron beam. Its lack of hydrogen distinguishes it from whitlockite.
Did you know?
Lunar merrillite is a major carrier of the KREEP component first recognised in the Apollo 12 soil.
Shock can turn merrillite into its high-pressure form, tuite.