An overview on Neptunite Jewelry and Gemstones. Covers details and essential information on the physical properties and characteristics of Neptunite gems.
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|Crystallography||Monoclinic; crystals prismatic, usually square in cross section, lustrous and very well formed.|
|Colors||Extremely dark red, appearing microscopically black. Transparent in small fragments, otherwise opaque.|
|Cleavage||Perfect 1 direction; fracture conchoidal; brittle.|
|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).|
|Pleochroism||yellow/ deep red.|
Optics: a= 1.690-1.691; β=1.693-1.700; γ=1.719—1.736.
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.