Phosphate mineral
Merrillite is a calcium phosphate mineral with the chemical formula Ca9NaMg(PO4)7. It is an anhydrous, sodium-rich member of the merrillite group of minerals.[4][5]
Mineral species, sub-group and group
Merrillite is a distinct mineral species but it also gives its name to a set of similar minerals, which together form the merrillite sub-group of minerals. The merrillite sub-group and the whitlockite sub-group together form the merrillite group of minerals.[6]
- Merrillite Group[6]
- Merrillite Sub-group
- Whitlockite Sub-group
In September 2022 the discovery of another merrillite group mineral, changesite–(Y), was announced,[7] but, as of September 2022[update], it is not yet clear where this new mineral sits in the merrillite group hierarchy.
Discovery and naming
Merrillite is named after George P. Merrill (1854–1929) of the Smithsonian Institution.[4] In 1915, Merrill had described the mineral from four meteorites: Alfianello, Dhurmsala, Pultusk and Rich Mountain. However, it was not until 1975 that it was recognized as distinct from whitlockite by the International Mineralogical Association.[4]
Occurrence
Merrillite is a very important constituent of extraterrestrial rocks.[citation needed] It occurs in lunar rocks and in meteorites (for example, pallasites and martian meteorites).[8]
In 2022, for the first time, merrillite was found in a terrestrial environment, as an inclusion in lower-mantle diamonds from Sorriso River, Juína, Brazil.[9]
References