| Pargasite | |
|---|---|
 Single crystal of pargasite, 1.5 cm long, on a matrix of white marble from Hunza Valley, Pakistan | |
| General | |
| Category | Inosilicates |
| Formula | NaCa2(Mg4Al)(Si6Al2)O22(OH)2 |
| IMA symbol | Prg [1] |
| Strunz classification | 9.DE.15 |
| Dana classification | 66.1.3a.12 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/m |
| Identification | |
| Color | Bluish green, grayish black, light brown |
| Crystal habit | Stout prismatic to tabular |
| Twinning | Simple and lamellar – common |
| Cleavage | {110} perfect |
| Fracture | Splintery |
| Mohs scale hardness | 5–6 |
| Luster | Vitreous |
| Diaphaneity | Translucent, will transmit light on thin edges. |
| Specific gravity | 3.04–3.17 |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.630 nβ = 1.640 nγ = 1.650 |
| Birefringence | δ = 0.020 max. |
| References | [2] [3] [4] [5] [6] |
Pargasite or pargasitic hornblende is a complex inosilicate mineral of the amphibole group with formula NaCa2(Mg4Al)(Si6Al2)O22(OH)2.
It was first described for an occurrence in Pargas, Finland in 1814 and named for the locality. [6]
It occurs in high temperature regional metamorphic rocks and in the skarns within contact aureoles around igneous intrusions. It also occurs in andesite volcanic rocks and altered ultramafic rocks. [3]
Pargasite is the main water-storage site in the uppermost mantle; however, it becomes unstable at depths greater than 90 km (56 mi). This has significant consequences for the water storage capacity, and the solidus temperature of the lherzolite of the upper mantle. [7]
