Neptunite | |
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![]() Neptunite crystals | |
General | |
Category | Phyllosilicate |
Formula (repeating unit) | KNa2Li(Fe2+,Mn2+)2Ti2Si8O24 |
IMA symbol | Npt[1] |
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 |
Luster | 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 | [2][3][4] |
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.[3] 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.[2]
The mineral is named for Neptune, Roman god of the sea because of its association with aegirine from Àgir, the Scandinavian sea-god.[3]
The Gemological Institute of America (GIA) identified an 11.78-carat faceted specimen as neptunite based on Raman spectroscopy.[6]
References
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ a b Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005). "Neptunite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved 14 March 2022.
- ^ a b c Neptunite, Mindat.org
- ^ Webmineral
- ^ Normand, Charles; Tarassoff, Peter (2006). Mineralogy and geology of the Poudrette quarry, Mont SaintHilaire, Quebec (PDF). Mineralogical Association of Canada. Retrieved 12 March 2022.
- ^ Cooper, Amy; Allen, Tara (Summer 2013). "Rare faceted neptunite". Gems & Gemology. 49 (2). Gemological Institute of America. Retrieved April 18, 2019.