Neptunite

Neptunite
Neptunite
	Neptunite crystals
General
Category	Phyllosilicate
Formula; (repeating unit)	KNa2Li(Fe2+,Mn2+)2Ti2Si8O24
IMA symbol	Npt
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

Neptunite is a silicate mineral with the formula K Na₂Li(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.

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[1] 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.

[Handbook-2] 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.

[Mindat-3] "Neptunite". Mindat.org.

[Webmin-4] Webmineral

[5] Normand, Charles; Tarassoff, Peter (2006). Mineralogy and geology of the Poudrette quarry, Mont SaintHilaire, Quebec (PDF). Mineralogical Association of Canada. Retrieved 12 March 2022.

[6] Cooper, Amy; Allen, Tara (Summer 2013). "Rare faceted neptunite". Gems & Gemology. 49 (2). Gemological Institute of America. Retrieved April 18, 2019.

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