Pargasite
Encyclopedia
Pargasite is a complex inosilicate mineral of the amphibole
group with formula NaCa2(Mg,Fe2+)4Al(Si6Al2)O22(OH)2.
It was first described for an occurrence in Pargas
, Finland
in 1814 and named for the locality.
It occurs in high temperature regional metamorphic rocks and in the skarn
s within contact aureoles around igneous intrusions. It also occurs in andesite
volcanic rocks and altered ultramafic rocks.
Pargasite is the main water-storage site in the uppermost mantle
, however it becomes unstable at depths greater than 90 km. This has significant consequences for the water storage capacity, and the solidus temperature of the lherzolite
of the upper mantle.
Amphibole
Amphibole is the name of an important group of generally dark-colored rock-forming inosilicate minerals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures.-Mineralogy:...
group with formula NaCa2(Mg,Fe2+)4Al(Si6Al2)O22(OH)2.
It was first described for an occurrence in Pargas
Pargas
Pargas is a former town and municipality in south-western Finland. On 1 January 2009, it was consolidated with Houtskär, Iniö, Korpo and Nagu to form the new town of Väståboland....
, Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
in 1814 and named for the locality.
It occurs in high temperature regional metamorphic rocks and in the skarn
Skarn
Skarn is an old Swedish mining term originally used to describe a type of silicate gangue, or waste rock, associated with iron-ore bearing sulfide deposits apparently replacing Archean age limestones in Sweden's Persberg mining district. In modern usage the term "skarn" has been expanded to refer...
s within contact aureoles around igneous intrusions. It also occurs in andesite
Andesite
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
volcanic rocks and altered ultramafic rocks.
Pargasite is the main water-storage site in the uppermost mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
, however it becomes unstable at depths greater than 90 km. This has significant consequences for the water storage capacity, and the solidus temperature of the lherzolite
Lherzolite
Lherzolite is a type of ultramafic igneous rock. It is a coarse grained rock consisting of 40 to 90% olivine along with significant orthopyroxene and lesser calcic chromium rich clinopyroxene. Minor minerals include chromium and aluminium spinels and garnets. Plagioclase can occur in lherzolites...
of the upper mantle.