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Magnesio-riebeckite [abbr. Mrbk ]

Year of discovery: 1957 (Alto Chapare District, Bolivia), 1957 (Japan)

Locality list: 38 localities of magnesio-riebeckite

• Na₂Mg₃Fe₂Si₈O₂₂(OH)₂
• Na₂(Mg,Fe)₃Fe₂Si₈O₂₂(OH)₂
• [][Na⁺₂][Mg²⁺₃][Fe³⁺₂][(OH)₂|Si₈O₂₂]^14-

• Class: Na amphibole subgroup < w(OH,F,Cl)-dominant amphibole group < Amphibole supergroup
• Class: Inosilicate (Double chain) - Hydroxide
• Radioactive: Very weak

• Mg => Fe: Riebeckite

• Fe => Al: Glaucophane

• NaSi => CaAl: Ferri-barroisite

• []Si => NaAl: Ferri-nybøite (Ferri-nyboite)

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

• Habit: Acicular, Prismatic

• Cleavage: Perfect on {110} (2 planes, 120 degree)
• Hardness: 5-5.5
• Density: 3.2

• System: Monoclinic
• Group: 2/m, C2/m
• Lattice: a=9.8, b=18.0, c=5.3, β=102.9