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Natroalunite

Year of discovery: 1911 (Red Mountain district, USA), 1935 (Japan)

Locality list: 28 localities of natroalunite

• NaAl₃(SO₄)₂(OH)₆
• (Na,K)Al₃(SO₄)₂(OH)₆
• [Na⁺][Al³⁺][Al³⁺₂][(OH)₆|(SO₄)₂]^10-

• Class: Alunite group < Alunite supergroup
• Class: Sulfate - Hydroxide
• Insoluble in: Water
• Electrical: Pyroelectric (Strong)

• Na => K: Alunite
• Na => Ca_0.5: Huangite
• Na => Ba_0.5: Walthierite
• Na => NH₄: Ammonioalunite

• Al => Fe: Natrojarosite

• Color: White, Pale brown
• Streak: White
• Luster: Vitreous
• Diaphaneity: Transparent

• Habit: Granular, Thin platy

• Cleavage: Distinct on {0001} (1 plane), Poor on {0112} (3 planes)
• Hardness: 3.5-4
• Density: 2.8

• System: Trigonal (1c, Natroalunite), Trigonal (2c, Natroalunite-2c) (Unit-cell polytype)
• Group: 3m, R3m
• Lattice: a=7.0, c=16.7