Neptunite Value, Price, and Jewelry Information

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

Home Gemstones Neptunite Value, Price, and Jewelry Information

By Joel E. Arem, Ph.D., FGA

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

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.

Joel E. Arem, Ph.D., FGA

Dr. Joel E. Arem has more than 60 years of experience in the world of gems and minerals. After obtaining his Ph.D. in Mineralogy from Harvard University, he has published numerous books that are still among the most widely used references and guidebooks on crystals, gems and minerals in the world.

Co-founder and President of numerous organizations, Dr. Arem has enjoyed a lifelong career in mineralogy and gemology. He has been a Smithsonian scientist and Curator, a consultant to many well-known companies and institutions, and a prolific author and speaker. Although his main activities have been as a gem cutter and dealer, his focus has always been education. joelarem.com

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Neptunite Properties

Absorption Spectrum

Not diagnostic.

Birefringence

0.029-0.045

Cleavage

Perfect 1 direction

Colors

Extremely dark red, appearing microscopically black.

Crystallography

Monoclinic; crystals prismatic, usually square in cross section, lustrous and very well formed.

Formula

(Na,K) ₂ (Fe ⁺² ,Mn)TiSi ₄ O ₁₂ (mangan-neptunite has Mn,Fe ² ).

Fracture

Conchoidal

Hardness

5-6

Luminescence

None.

Luminescence Present

Luster

Vitreous.

Optic Sign

Biaxial +

Optics

a= 1.690-1.691; β = 1.693-1.700; γ = 1.719-1.736. Biaxial (+).

Pleochroism

Yellow/deep red.

Refractive Index

1.690-1.736

Specific Gravity

3.19-3.23

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.

Transparency

Transparent in small fragments, otherwise opaque.

Variety of

Gemstones for Collectors

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