Mineral Information and Data:

Arfvedsonite
NaNa2(Fe2+4Fe3+)Si8O22(OH)2 [CNMNC approved formula]

Named after the Swedish chemist, J. A. Arfvedson (1792-1841). Named as Arfwedsonite in 1823.

IMA status : Approved Species 1997 ()
CLASSIFICATION 
Dana
(8th edition) :
66.01.03c.09  
  (66) Inosilicate Double-Width Unbranched Chains, W=2
  (66.01) with P=2 amphibole configuration
  (66.01.03c) Group 4, the sodic amphiboles
  
Nickel-Strunz
(10th edition) :
09.DE.25
  (09) Silicates
  (09.D) Inosilicates* Structural terminology per Liebau (1985)
  (09.DE) with 2-periodic double chains, Si4O11; Clinoamphiboles
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Unit cell: a = 10.007Å, b = 18.077Å, c = 5.332Å β = 104.1°
Crystal Habit: Crystals short to long prismatic, often tabular; prismatic aggregates and radiating fibrous clusters
  
Color: Greenish black
Diaphaneity: Translucent to nearly opaque
Luster: Vitreous
Hardness (Mohs): 5 - 6
Measured Density: 3.37 - 3.50 g/cm3
Cleavage: 2; {110} perfect, {010} parting
Tenacity: Brittle
Fracture: Uneven
Streak: Dark bluish grey-green
  
Polymorphism and Series: Forms a series with magnesio-arfvedsonite.
Geologic Setting: Common in alkalic granites and other alkalic plutonic rocks and pegmatites.
Mineral Association: Nepheline, albite, aegirine, riebeckite, katophorite, magnesio-katophorite, quartz
  

 

Arfvedsonite
Arfvedsonite with aegirine on orthoclase
Origin: Mt. Maloso, Malawi
Sample size: 6.5 x 5 x 4 cm
Photo: Rob Lavinsky

 

Arfvedsonite
(zoom-in of above)

 

Arfvedsonite
2-4 cm long arvedsonite crystals with 2-6 mm eudialyte
and yellow-brown rinkite
Origin: Kangersluarssak, Ilimaussaq Intrusion, Greenland, Denmark
Sample size: 5 x 6 cm
Photo: Diederik Visser

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