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Merrillite

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[edit]

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
    • Ferromerrillite
    • Keplerite
    • Matyhite
    • Merrillite
  • Whitlockite Sub-group
    • Hedegaardite
    • Strontiowhitlockite
    • Whitlockite
    • Wopmayite

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[edit]

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[edit]

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 inclusioninlower-mantle diamonds from Sorriso River, Juína, Brazil.^[9]

References[edit]

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