Neptunite Value, Price, and Jewelry Information

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By Didier Descouens (Own work) [CC-BY-3.0], via Wikimedia Commons

An overview on Neptunite Jewelry and Gemstones. Covers details and essential information on the physical properties and characteristics of Neptunite gems.

Neptunite Information

Data Value
Name Neptunite
Stone Sizes Neptunite is opaque except in minute fragments, from which tiny faceted stones (under 1 carat) of deep red color have been cut. The color intensity limits the practical size of gemstones; opaque blackish stones in the 20-30 carat range could be cut but would not display the lovely red color neptunite displays in smaller fragments.
Formula (Na,K)2(Fe+2,Mn)TiSi4O12 (mangan-neptunite has Mn,Fe2).
Colors Extremely dark red, appearing microscopically black.
Fracture Conchoidal
Hardness 5-6
Cleavage Perfect 1 direction
Crystallography Monoclinic; crystals prismatic, usually square in cross section, lustrous and very well formed.
Crystallographic Forms
Refractive Index 1.690-1.736
Birefringence 0.029-0.045
Luminescence None.
Luminescence Present No
Absorption Spectrum Not diagnostic.
Pleochroism Yellow/deep red.
Optics = 1.690-1.691; β = 1.693-1.700; γ = 1.719-1.736. Biaxial (+).
Optic Sign Biaxial +
Luster Vitreous.
Specific Gravity 3.19-3.23
Transparency Transparent in small fragments, otherwise opaque.

Optics: a= 1.690-1.691; β=1.693-1.700; γ=1.719—1.736.

Biaxial (+)

Occurrence: In alkaline rocks and carbonatites but most especially embedded in natrolite in San Benito County, California, where it occurs in spectacular crystals associated with benitoite and joaquinite.

Narsarsuk, Julianhaab district, Greenland.

Mt. Ste. Hilaire, Quebec, Canada.

Kola Peninsula, USSR: mangan-neptunite.

San Benito County, California.

Name: For Neptune, god of the sea in mythology, because it was found associated with aegirine, named after Aegir, Scandinavian god of the sea.

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