Narsarsukite

Narsarsukite is a rare silicate mineral with either the chemical formula Na2(Ti,Fe3+)Si4(O,F)11[2] or Na4(Ti,Fe)4[Si8O20](O,OH,F)4.[1]

Narsarsukite
Narsarsukite-20220.jpg
1.3 cm crystal of narsarsukite from Mont Saint-Hilaire
General
CategorySilicate mineral
Formula
(repeating unit)		Na4(Ti,Fe)4[Si8O20](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
LusterVitreous, 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]

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)

This article uses material from the Wikipedia article
 Metasyntactic variable, which is released under the 
Creative Commons
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Note

This article uses material from the Wikipedia article
 Metasyntactic variable, which is released under the 
Creative Commons
Attribution-ShareAlike 3.0 Unported License.