Nepheline

Nepheline is named after Greek "nephele" - a cloud, alluding to the cloudy appearance that develops when the mineral is immersed in strong acid.

Nepheline forms transparent to nearly opaque prismatic crystals, usually colourless, but can be coloured gray, red, green, brown, yellow from various impurities.

Transparent colourless material has been faceted.
General Information
Varieties/Types:
Elaeolite - Old name for massive, oily/greasy variety of Nepheline.
Chemical Formula
Na
 
3
(Na,K)Al
 
4
Si
 
4
O
 
16
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Photos of natural/un-cut material from mindat.org
Physical Properties of Nepheline
Mohs Hardness5 to 6
Walter Schumann, Gemstones of the world (2001)
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Specific Gravity2.55 to 2.65
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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TenacityBrittle
Arthur Thomas, Gemstones (2009)
Cleavage QualityImperfect
Arthur Thomas, Gemstones (2009)
FractureSub-Conchoidal
Arthur Thomas, Gemstones (2009)
Optical Properties of Nepheline
Refractive Index1.529 to 1.547
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Optical CharacterUniaxial/-
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Birefringence0.003 to 0.005
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Colour
Colour (General)Colourless, white, gray, greenish-gray, yellowish, reddish, blue-green, brownish. Chatoyant
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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TransparencyTransparent,Translucent,Opaque
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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LustreVitreous,Greasy
Arthur Thomas, Gemstones (2009)
Fluorescence & other light emissions
Fluorescence (Long-Wave UV)Some German specimens may show a light blue and some from Ontario an orange fluorescence
Michael O’Donoghue, Gems, Sixth Edition (2006)
Crystallography of Nepheline
Crystal SystemHexagonal
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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HabitPrismatic
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Geological Environment
Where found:Nepheline occurs in alkalic rocks, including nepheline syenites and pegmatites associated with them, also in gneisses.
Michael O’Donoghue, Gems, Sixth Edition (2006)
Inclusions in Nepheline
Partially healed fractures, mirror-like inclusions - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p 7
Further Information
Mineral information:Nepheline information at mindat.org
Significant Gem Localities
Canada
 
  • Ontario
    • Hastings Co.
      • Dungannon Township
Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 433
Germany
 
  • Baden-Württemberg
    • Odenwald
      • Eberbach
        • Katzenbuckel
Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 433
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