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Neptunite.

(K,Na)₂(Fe,Mg,Ca,)₂(Ti,Si)₄O₁₂. TiO₂ = 18%.

Monoclinic. Habit prismatic.

G = 3·23. H = 5¹⁄₂. Black, red in flakes. Translucent to opaque.

Narsarsuk, Greenland.