Prehnite

Big Photo

South Africa
11.73 carats
© gemselect.com

Prehnite is named after Dutch Colonel Hendrik Von Prehn, and was first described in 1789 for an occurrence in Haslach, Harzburg and Oberstein, Germany.

Individual crystals are rare. Faceted gems are seldom fully transparent and don't show "fire". Prehnite is usually cut into cabochons or carved.

Extensive deposits of gem quality prehnite occur near Wave Hill Station in the central Northern Territory, of Australia.

Prehnite cat's is known.

Prehnite Gemstones by Colour

This table shows the variety of hues this gemstone can be found in. Click on a photo for more information.
 
 

Prehnite Gemstones by Size

This table shows distribution of Prehnite gemstone sizes that are listed on this site. This can give a good indication as to the general availability of this gemstone in different sizes.
Contributed photos
Lightest:1.11 cts
Heaviest:40.17 cts
Average:8.70 cts
Total photos:54
Do you have a larger Prehnite? Why not upload a photo?
1.11ct to 5.02ct5.02ct to 8.92ct8.92ct to 12.83ct12.83ct to 16.73ct16.73ct to 20.64ct20.64ct to 24.55ct24.55ct to 28.45ct28.45ct to 32.36ct32.36ct to 36.26ct36.26ct to 40.17ct
General Information
Chemical Formula
Ca
 
2
Al
 
2
Si
 
3
O
 
10
(OH)
 
2
Michael O’Donoghue, Gems, Sixth Edition (2006)
More from other references
Photos of natural/un-cut material from mindat.org
Physical Properties of Prehnite
Mohs Hardness6 to 6.5
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Specific Gravity2.80 to 2.95
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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TenacityBrittle
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Cleavage QualityGood
Walter Schumann, Gemstones of the world (2001)
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FractureUneven
Walter Schumann, Gemstones of the world (2001)
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Optical Properties of Prehnite
Refractive Index1.611 to 1.673
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Optical CharacterBiaxial/+
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Birefringence0.021 to 0.039
Walter Schumann, Gemstones of the world (2001)
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PleochroismAbsent
Walter Schumann, Gemstones of the world (2001)
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DispersionNone
Walter Schumann, Gemstones of the world (2001)
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ChatoyancyYes
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Colour
Colour (General)Oily yellowish-(greenish)
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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TransparencyTranslucent
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) Usually translucentMore from other references
LustreVitreous,Pearly
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Fluorescence & other light emissions
Fluorescence (General)None
Walter Schumann, Gemstones of the world (2001)
Crystallography of Prehnite
Crystal SystemOrthorhombic
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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HabitRadiating fibrous aggregate
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Geological Environment
Where found:Occurs as a secondary or hydrothermal mineral in veins or cavities in mafic volcanic rocks or in granite gneisses or syenites
Michael O’Donoghue, Gems, Sixth Edition (2006)
Further Information
Mineral information:Prehnite information at mindat.org
Significant Gem Localities
Australia
 
  • Northern Territory
    • Victoria-Daly Region
Gemstones of the world, W. Schumann, 2001, p.188
Canada
 
  • Québec
    • Estrie
      • Les Sources RCM
        • Asbestos
Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 440
USA
 
  • Virginia
    • Fairfax Co.
      • Culpeper Basin
        • Centreville
Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 440
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