Neptunite

Neptunite crystals

General
Category| Phyllosilicate
Formula
(repeating unit)| KNa2Li(Fe2+,Mn2+)2Ti2Si8O24
Strunz classification| 9.EH.05
Dana classification| 70.04.01.01
Crystal system| Monoclinic
Crystal class| Domatic (m)
(same H-M symbol)
Space group| Cc
Unit cell| a = 16.427(2), b = 12.478(2)
c = 9.975(1) Å; β = 115.56(1)°; Z = 4
Identification
Color| Black; deep red-brown in thin fragments
Crystal habit| Prismatic or tabular
Twinning| Interpenetrant on {301}
Cleavage| {110} good
Fracture| Conchoidal
Tenacity| Brittle
Mohs scale hardness| 5–6
|re|er}}| Vitreous
Streak| Brown to red brown
Diaphaneity| Nearly opaque
Specific gravity| 3.19–3.23
Optical properties| Biaxial (+)
Refractive index| nα = 1.69–1.6908,
nβ = 1.6927–1.7,
nγ = 1.7194–1.736
Birefringence| 0.0294–0.0452
Pleochroism| x = yellow-orange, y = orange, z = deep red
2V angle| 36° to 49°
Other characteristics| Piezoelectric
References| [1][2][3]

Neptunite is a silicate mineral with the formula KNa2Li(Fe2+, Mn2+)2Ti2Si8O24. With increasing manganese it forms a series with mangan-neptunite. Watatsumiite is the variety with vanadium replacing the titanium in the formula.

It was first described in 1893 for an occurrence in the Narssârssuk pegmatite of West Greenland.[2] It is also found within natrolite veins in glaucophane schist within serpentinite in San Benito County, California, US. It also occurs in Mont Saint-Hilaire, Quebec[5] and in the Kola Peninsula of Russia .[1]

The mineral is named for Neptune, Roman god of the sea because of its association with aegirine from Àgir, the Scandinavian sea-god.[2]

The Gemological Institute of America (GIA) identified an 11.78-carat faceted specimen as neptunite based on Raman spectroscopy.[6]

## References

1. ↑ 1.0 1.1 Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005). "Neptunite". Mineral Data Publishing. http://www.handbookofmineralogy.org/pdfs/neptunite.pdf.
2. ↑ 2.0 2.1 2.2 Neptunite, MinDat.org, http://www.mindat.org/show.php?id=2883
3. ↑ Webmineral
4. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W.
5. ↑ Normand, Charles; Tarassoff, Peter (2006). Mineralogy and geology of the Poudrette quarry, Mont SaintHilaire, Quebec. Mineralogical Association of Canada. https://www.mcgill.ca/redpath/files/redpath/guidebook_4a_final2.pdf. Retrieved 12 March 2022.
6. ↑ Cooper, Amy; Allen, Tara (Summer 2013). "Rare faceted neptunite". Gems & Gemology (Gemological Institute of America) 49 (2). https://www.gia.edu/gems-gemology/summer-2013-labnotes-rrare-faceted-neptunite. Retrieved April 18, 2019.

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