Merrillite is a calcium

phosphate mineral Phosphate minerals contain the tetrahedrally coordinated phosphate (PO43−) anion along sometimes with arsenate (AsO43−) and vanadate (VO43−) substitutions, and chloride (Cl−), fluoride (F−), and hydroxide (OH−) anions that also fit ...

with the chemical formula Ca₉NaMg(PO₄)₇. 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 In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

'' 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–(Y), was announced, but, , 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 George Perkins Merrill (May 31, 1854 – August 15, 1929) was an American geologist, notable as the head curator from 1917 to 1929 of the Department of Geology, United States National Museum (now the National Museum of Natural History of the Smith ...

(1854–1929) 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 Founded in 1958, the International Mineralogical Association (IMA) is an international group of 40 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 5000 plus known mineral species. Th ...

Occurrence

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

pallasite The pallasites are a class of stony–iron meteorite. Structure and composition It consists of centimetre-sized olivine crystals of peridot quality in an iron-nickel matrix. Coarser metal areas develop Widmanstätten patterns upon etching. Mino ...

s and

martian meteorite A Martian meteorite is a rock that formed on Mars, was ejected from the planet by an impact event, and traversed interplanetary space before landing on Earth as a meteorite. , 277 meteorites had been classified as Martian, less than half a perce ...

s). In 2022, for the first time, merrillite was found in a terrestrial environment, as an inclusion in lower-mantle diamonds from

Sorriso River Sorriso is a municipality in the state of Mato Grosso in the Central-West Region of Brazil. The name of the city means literally "smile", but it actually came from the Italian immigrants who only cultivated rice in the region: "only rice" = "só ...

Juína Juína is a municipality in the state of Mato Grosso Mato Grosso ( – lit. "Thick Bush") is one of the states of Brazil, the third largest by area, located in the Central-West region. The state has 1.66% of the Brazilian population and is ...

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

References

Phosphate minerals Meteorite minerals {{phosphate-mineral-stub