Merrillite

Merrillite
General
Category Phosphate mineral
Formula
(repeating unit)		 Ca9NaMg(PO4)7
Strunz classification 08.AC.45
Crystal symmetry Trigonal ditrigonal pyramidal
H-M symbol: (3m)
Space group: R 3c
Unit cell a = 10.362 Å, c = 37.106 Å; Z=6
Identification
Color Colorless to white
Crystal habit Occurs as anhedral grains
Crystal system Trigonal
Cleavage Poor - indistinct
Tenacity Brittle
Luster Vitreous
Specific gravity 3.1 (measured)
Optical properties Uniaxial (-)
Refractive index nε=1.62, nω=1.623
Birefringence 0.0030
References [1][2]

Merrillite is a calcium phosphate mineral with the chemical formula Ca9NaMg(PO4)7. It is an anhydrous, sodic member of the whitlockite group.[2]

Discovery and naming

The mineral is named after George P. Merrill (1854-1929) of the Smithsonian Institution.[2] Merrill had described the mineral from four meteorites in 1915: the Alfianello, Dhurmsala, Pultusk, and Rich Mountain meteorites. The mineral was not recognized as distinct from whitlockite, however, by the IMA until 1975.[2]

Occurrence

Merrillite is a very important constituent of extraterrestrial rocks. It occurs in pallasites, lunar rocks, martian meteorites, and many other meteorite groups.[3]

References

  1. ↑ Merrillite data on Webmineral
  2. ↑ 2.0 2.1 2.2 2.3 "Merrillite". Mindat. Retrieved 6 January 2013.
  3. ↑ Jolliff, Bradley L.; John M. Hughes; John J. Freeman & Ryan A. Zeigler (2006). "Crystal chemistry of lunar merrillite and comparison to other meteoritic and planetary suites of whitlockite and merrillite". American Mineralogist 91: 1583–1595. doi:10.2183/am.2006.2185.