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Dominant species
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Arfvedsonite
Arfvedsonite
Chemical
Formula
[Na][Na2][(Fe2+)4Fe3+][(OH)2|Si8O22]
Species
Silicates
Crystal
System
Monoclinic
Mohs
Scale
5-6
Specific
Gravity
3.3–3.5
Color
Black, deep green on thin edges
Streak
Deep bluish gray, gray-green
Luster
Vitreous
Refractive
Index
n = 1.652 - 1.699 n = 1.660 - 1.705 n = 1.666 - 1.708
Diaphaneity
Translucent, Opaque
Cleavage
PerfectPerfect on
Fracture
Irregular/Uneven
Crystal Habit:Fibrous, radial prismatic aggregates
Geological Setting:Alkalic granites and other alkalic rocks
Arfvedsonite is a sodium amphibole mineral with composition: [Na][Na2][(Fe2+)4Fe3+][(OH)2|Si8O22]. It crystallizes in the monoclinic prismatic crystal system and typically occurs as greenish black to bluish grey fibrous to radiating or stellate prisms.
It is a rather rare mineral occurring in nepheline syenite intrusions and agpaitic (peralkaline) pegmatites and granites as the Golden Horn batholith in Okanogan County, Washington (type locality for zektzerite). Occurrences include Mont Saint-Hilaire, Quebec, Canada; the Ilímaussaq complex in Southern Greenland; and in pegmatites of the Kola Peninsula, Russia. Its mineral association includes nepheline, albite, aegirine, riebeckite, katophorite and quartz.
Arfvedsonite was discovered in 1823 and named for the Swedish chemist Johan August Arfwedson (1792–1841).