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CategorySilicate mineral
Chemical formulaKNa2Li(Fe2+,Mn2+)2Ti2Si8O24
ColorBlack, red
Crystal habitPrismatic or tabular
Crystal systemMonoclinic
TwinningInterpenetrant on {301}
Cleavage{110} good
Mohs Scale hardness5-6
Refractive indexα=1.69-1.6908, β=1.6927-1.7, γ=1.7194-1.736
Optical PropertiesBiaxial (+) 2V = 36° to 49°
Pleochroismx=yellow-orange, y=orange, z=deep red
StreakBrown to red brown
Specific gravity3.19 - 3.23
DiaphaneityNearly opaque
Other CharacteristicsPiezoelectric

Neptunite is a silicate mineral with the formula KNa2Li(Fe2+,Mn2+)2Ti2Si8O24. With increasing manganese it forms a series with mangan-neptunite. Watatsumiite is the variety with vanadium replacing the titanium in the formula.

It was first described in 1893 for an occurrence in the Narssârssuk pegmatite of West Greenland. It is also found within natrolite veins in glaucophane schist within serpentinite in San Benito County, California, USA. The mineral is named for Neptune, Roman god of the sea because of its association with aegirine from Àgir, the Scandinavian sea-god. It also occurs in Mont Saint-Hilaire, Quebec and in the Kola Peninsula of Russia.


  • Mindat with location data
  • Webmineral
  • Mineral Handbook
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Neptunite". A list of authors is available in Wikipedia.
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