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.
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	a = 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.