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Arfvedsonite [abbr. Arf ]

Year of discovery: 1923 (Kangerluarsuk Fjord, Greenland), 1928 (Japan)

Locality list: 15 localities of arfvedsonite

• Na₃Fe₅Si₈O₂₂(OH)₂
• [Na⁺][Na⁺₂][Fe²⁺₄][Fe³⁺][(OH)₂|Si₈O₂₂]^14-

• Class: Na amphibole subgroup < w(OH,F,Cl)-dominant amphibole group < Amphibole supergroup
• Class: Inosilicate (Double chain) - Hydroxide
• Insoluble in: HCl

• Na => K: Potassic-arfvedsonite
• Na => []: Riebeckite

• Fe²⁺ => Mg: Magnesio-arfvedsonite (Series)
• Fe²⁺ => Mn: Mangano-arfvedsonite

• Fe³⁺ => Al: Ferro-eckermannite

• Na₂ => Ca: Ferro-ferri-winchite

• NaSi => CaAl: Ferro-ferri-katophorite

• Si₈ => Si₇Al: Ferro-ferri-nybøite (Ferro-ferri-nyboite)

• Color: Dark blue-Black
• Streak: Dark blue
• Luster: Vitreous
• Diaphaneity: Translucent-Opaque

• Habit: Fibrous, Prismatic

• Cleavage: Perfect on {110} (2 planes, 120 degree), Parting on {010} (1 plane)
• Hardness: 5-6
• Density: 3.5

• System: Monoclinic
• Group: 2/m, C2/m
• Lattice: a=10.0, b=18.1, c=5.3, β=104.1