Chemistry:Narsarsukite

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Narsarsukite
Narsarsukite-20220.jpg
1.3 cm crystal of narsarsukite from Mont Saint-Hilaire
General
CategorySilicate mineral
Formula
(repeating unit)
Na
4
(Ti,Fe)
4
[Si
8
O
20
](O,OH,F)
4
[1]
Strunz classification9.DJ.05
Crystal systemTetragonal
Crystal classDipyramidal (4/m)
H-M symbol: (4/m)
Space groupI4/m
Unit cella = 10.72, c = 7.95 [Å]; Z = 4
Identification
ColorHoney to lemon-yellow, reddish brown, brownish gray, tan, pink; may be green from inclusions; may show color zoning
Crystal habitOccurs as flat tabular to equant, striated crystals In divergent, radiating groups; massive
CleavageGood on {100} and {110}
FractureUneven to subconchoidal
TenacityBrittle
Mohs scale hardness5.5 - 7
|re|er}}Vitreous, pearly on {110}
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.64-2.83
Optical propertiesUniaxial (+)
Refractive indexnω = 1.609 nε = 1.630
Birefringenceδ = 0.021
PleochroismWeak; O = colorless to yellow; E = colorless to honey-yellow
References[2][1][3]

Narsarsukite is a rare silicate mineral with either the chemical formula Na
2
(Ti,Fe3+)Si
4
(O,F)
11
[2] or Na
4
(Ti,Fe)
4
[Si
8
O
20
](O,OH,F)
4
.[1]

It was first described in 1900 for an occurrence in the Narsarsuk pegmatite in the Ilimaussaq intrusive complex of West Greenland.[1] It has also been reported from a syenite which intruded limestone in the Sweetgrass Hills, Montana, and within hornfels and marble xenoliths in the alkalic intrusive of Mont Saint-Hilaire, Quebec.[2] It occurs associated with aegirine, microcline, albite, elpidite, epididymite, taeniolite, pectolite, calcite, galena and quartz.[2]

Narsarsukite from Whitlash, Liberty County, Montana {size: 5.6 x 5.4 x 5.1 cm)

References

  1. Jump up to: 1.0 1.1 1.2 1.3 Narsarsukite on Mindat.org
  2. Jump up to: 2.0 2.1 2.2 2.3 Handbook of Mineralogy
  3. Narsarsukite data on Webmineral
  4. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode2021MinM...85..291W.