Merrillite


Merrillite is a calcium phosphate mineral with the chemical formula Ca9NaMg7. It is an anhydrous, sodium-rich member of the merrillite group of minerals.

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.
  • Merrillite Group
  • *Merrillite Sub-group
  • **Ferromerrillite
  • **Keplerite
  • **Matyhite
  • **Merrillite
  • *Whitlockite Sub-group
  • **Hedegaardite
  • **Strontiowhitlockite
  • **Whitlockite
  • **Wopmayite
In September 2022 the discovery of another merrillite group mineral, changesite–, was announced, but, as of 2022, 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 of the Smithsonian Institution. 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.

Occurrence

Merrillite is a very important constituent of extraterrestrial rocks. It occurs in lunar rocks and in meteorites.
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.