| Acuminite | |
|---|---|
| General | |
| Category | Halide mineral |
| Formula | SrAlF4OH·(H2O) |
| IMA symbol | Acu[1] |
| Strunz classification | 3.CC.10 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/c |
| Unit cell | a = 13.223, b = 5.175 c = 14.251 [Å]; β = 11.61°; Z = 8 |
| Identification | |
| Color | White |
| Crystal habit | Clusters of acute dipyramidal Spearhead shaped crystals |
| Twinning | Contact on {100} |
| Cleavage | Perfect on {001} |
| Mohs scale hardness | 3.5 |
| Luster | Vitreous |
| Diaphaneity | Transparent |
| Specific gravity | 3.295 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.451 nβ = 1.453 nγ = 1.462 - 1.463 |
| References | [2][3][4] |
Acuminite is a rare halide mineral with chemical formula: SrAlF4(OH)·(H2O). Its name comes from the Latin word acumen, meaning "spear point". Its Mohs scale rating is 3.5.
Acumenite has only been described from its type locality of the cryolite deposit in Ivigtut, Greenland.[2]
