Merrillite
Merrillite is a calcium phosphate mineral with the chemical formula Ca9NaMg(PO4)7. It is an anhydrous, sodic member of the whitlockite group.[3]
| Merrillite | |
|---|---|
| General | |
| Category | Phosphate mineral |
| Formula (repeating unit) | Ca9NaMg(PO4)7 |
| Strunz classification | 8.AC.45 |
| Crystal system | Trigonal |
| Crystal class | Ditrigonal pyramidal (3m) (same H-M symbol) |
| Space group | R3c |
| Unit cell | a = 10.362 Å, c = 37.106 Å; Z = 6 |
| Identification | |
| Color | Colorless to white |
| Crystal habit | Occurs as anhedral grains |
| 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][3] |
Discovery and naming
The mineral is named after George P. Merrill (1854–1929) of the Smithsonian Institution.[3] 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.[3]
Occurrence
Merrillite is a very important constituent of extraterrestrial rocks. It occurs in pallasites, lunar rocks, martian meteorites, and many other meteorite groups.[4]
References
- Mineralienatlas
- Merrillite data on Webmineral
- "Merrillite". Mindat. Retrieved 6 January 2013.
- 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:10.2138/am.2006.2185.
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