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Riebeckite [abbr. Rbk ]

Year of discovery: 1888 (Socotra island, Yemen), 1913 (Japan)

Locality list: 50 localities of riebeckite

• Na₂Fe₅Si₈O₂₂(OH)₂
• [][Na⁺₂][Fe²⁺₃][Fe³⁺₂][(OH)₂|(Si₄O₁₁)₂]^14-

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

• [] => Na: Arfvedsonite
• [] => K: Potassic-arfvedsonite
• [] => Ca: Ferro-ferri-richterite

• Na => Li: Ferro-ferri-holmquistite

• Na₂ => Fe: Ferro-anthophyllite, Grunerite, Proto-ferro-anthophyllite
• Na₂ => Mn: Mangano-grunerite, Proto-ferro-suenoite
• Na₂ => Ca: Ferro-actinolite

• Fe²⁺ => Mg: Magnesio-riebeckite

• Fe³⁺ => Al: Ferroglaucophane

• []Fe²⁺ => NaLi: Ferro-ferri-leakeite

• NaSi => CaAl: Ferro-ferri-barroisite

• []Si => NaAl: Ferro-ferri-nybøite (Ferro-ferri-nyboite)
• []Si => CaAl: Ferro-ferri-katophorite

• Color: Pale blue, Bluish black
• Streak: Pale bluish gray
• Luster: Vitreous
• Diaphaneity: Translucent-Opaque

• Habit: Acicular, Prismatic

• Cleavage: Perfect on {110} (2 planes, 120 degree)
• Hardness: 5-5.5
• Density: 3.4

• System: Monoclinic
• Group: 2/m, C2/m
• Lattice: a=9.8, b=18.0, c=5.3, β=103.6

Synonym: Crocidolite