| Merrillite | |
|---|---|
| General | |
| Category | Phosphate mineral |
| Formula (repeating unit) | 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]