Pargasite
Pargasite
Amphibole, double chain inosilicate mineral
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]