Neptunite
Neptunite | |
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![]() Neptunite crystals | |
General | |
Category | Phyllosilicate |
Formula (repeating unit) | KNa2Li(Fe2+,Mn2+)2Ti2Si8O24 |
Strunz classification | 9.EH.05 |
Dana classification | 70.04.01.01 |
Crystal system | Monoclinic |
Crystal class | Domatic (m) (same H-M symbol) |
Space group | Cc |
Unit cell | a = 16.427(2), b = 12.478(2) c = 9.975(1) Å; β = 115.56(1)°; Z = 4 |
Identification | |
Color | Black; deep red-brown in thin fragments |
Crystal habit | Prismatic or tabular |
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 (+) |
Refractive index | nα=1.69-1.6908, nβ=1.6927-1.7, nγ=1.7194-1.736 |
Birefringence | 0.0294-0.0452 |
Pleochroism | x=yellow-orange, y=orange, z=deep red |
2V angle | 36° to 49° |
Other characteristics | Piezoelectric |
References | [1][2][3] |
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.[2] It is also found within natrolite veins in glaucophane schist within serpentinite in San Benito County, California, US. It also occurs in Mont Saint-Hilaire, Quebec and in the Kola Peninsula of Russia.[1]
The mineral is named for Neptune, Roman god of the sea because of its association with aegirine from Àgir, the Scandinavian sea-god.[2]
The Gemological Institute of America (GIA) identified an 11.78-carat faceted specimen as neptunite based on Raman spectroscopy.[4]
![](http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Neptunite.jpg/170px-Neptunite.jpg)