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Nontronite

Year of discovery: 1827 (Saint-Pardoux-la-Rivière, France), 1913 (Japan)

Locality list: 67 localities of nontronite

• Na_0.33Fe₂(Si,Al)₄O₁₀(OH)₂,nH₂O
• [Na⁺_0.33][Fe³⁺₂][(OH)₂|(Si,Al)₄O₁₀],nH₂O

• Class: Dioctahedral < Smectite group < Mica supergroup
• Class: Phyllo-Aluminosilicate - Hydroxide - Hydrate
• Soluble in: HCl (Gel residue)
• Substitution pseudomorph: Replace Fayalite. (Iddingsite)

• Fe => Al: Montmorillonite
• Fe => Mg_1.5: Stevensite

• Color: Yellowish green, Grayish green, Brown
• Streak: Pale yellow
• Luster: Resinous
• Diaphaneity: Opaque

• Habit: Earthy

• Cleavage: Perfect on {001} (1 plane)
• Hardness: 1.5-2
• Density: 2.3

• System: Monoclinic
• Group: 2/m, C2/m
• Lattice: a=5.2, b=9.1, c=15.3, β=90.0