Pargasite

Pargasite
Single crystal of pargasite, 1.5 cm long, on a matrix of white marble from Hunza Valley, Pakistan
General
Category	Inosilicates
Formula (repeating unit)	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]

It is used as a gemstone.[8][9]

See also

• Anyolite

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. Mineralienatlas
3. "Pargasite" (PDF). Handbook of Mineralogy (pdf). Mineralogical Society of America. Retrieved 2012-12-17.
4. "IMA Master List". Archived from the original on 2015-01-05. Retrieved 2014-05-12.
5. "Pargasite". mindat.org. Retrieved 2012-12-17.
6. "Pargasite Mineral Data". webmineral.com. Retrieved 2012-12-17. (Java plugin required)
7. Green, D H; Hibberson, W O; Kovacs, Istvan; Rosenthal, A (23 September 2010). "Water and its influence on the lithosphere–asthenosphere boundary". Nature. 467 (7314): 448–451. Bibcode:2010Natur.467..448G. doi:10.1038/nature09369. PMID 20865000. S2CID 4393352. (subscription required)
8. Dedeyne, Roger; Quintens, Evo (2007). Tables of gemstone identification (1st ed.). Gent, Belgium: Glirico. p. 169. ISBN 9789078768012. Retrieved 5 November 2020.
9. "Amethyst Crystals and Meaning Healing Properties". nacrystal.com. 2022-07-11. Retrieved 2023-02-10.

Spinel and pargasite on marble, Luc Yen District, Vietnam. Specimen size: 4.5 × 3.5 × 3.5 cm.