Neptunite Value, Price, and Jewelry Information

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 Value

The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.

Neptunite Information

Crystallography Monoclinic; crystals prismatic, usually square in cross section, lustrous and very well formed.
Refractive Index 1.690-1.736
Colors Extremely dark red, appearing microscopically black.
Luster Vitreous.
Fracture Conchoidal
Hardness 5-6
Specific Gravity 3.19-3.23
Birefringence 0.029-0.045
Cleavage Perfect 1 direction
Stone SizesNeptunite 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.
Luminescence None.
Transparency Transparent in small fragments, otherwise opaque.
Absorption Spectrum Not diagnostic.
Formula(Na,K)2(Fe+2,Mn)TiSi4O12 (mangan-neptunite has Mn,Fe2).
Pleochroism Yellow/deep red.
Optics = 1.690-1.691; β = 1.693-1.700; γ = 1.719-1.736. Biaxial (+).

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.