Merrillite
| Merrillite | |
|---|---|
| General | |
| Category | Phosphate mineral |
| Formula | Ca9NaMg(PO4)7 |
| IMA symbol | Mer[1] |
| 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 | [2][3][4] |
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 | edit source]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
- Merrillite Sub-group
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 | edit source]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 | edit source]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 inclusion in lower-mantle diamonds from Sorriso River, Juína, Brazil.[9]
References
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- ^ Mineralienatlas
- ^ Merrillite data on Webmineral
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