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Neptunite
General
Category Silicate mineral
Chemical formula KNa2Li(Fe2+,Mn2+)2Ti2Si8O24
Identification
Color Black, red
Crystal habit Prismatic or tabular
Crystal system Monoclinic
Twinning Interpenetrant on {301}
Cleavage {110} good
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 5-6
Luster Vitreous
Streak Brown to red brown
Diaphaneity Nearly opaque
Specific gravity 3.19 - 3.23
Optical properties Biaxial (+) 2V = 36° to 49°
Refractive index α=1.69-1.6908, β=1.6927-1.7, γ=1.7194-1.736
Birefringence 0.0294-0.0452
Pleochroism x=yellow-orange, y=orange, z=deep red
Other characteristics Piezoelectric

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.

References[]

it:Neptunite

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