Cordierite (Iolite)

Big Photo

Madagascar
4.26 carats
© gemselect.com

Cordierite was discovered in 1813 and is named after the French geologist Louis Cordier. It is also called Iolite (Greek - violet), and is sometimes misleadingly termed "Water sapphire".

Cordierite is famous for its remarkable trichroism: deep violet-blue (looking down the length of the prism) - blue-gray or yellowish-brown (when viewed through the sides). Oriented correctly Cordierite can be cut into attractive deep blue faceted gems.

"Bloodshot Iolite" originates from Sri Lanka. It has a distinct reddish sheen or aventurescence, caused by hematite and goethite inclusions.

Varieties with Cat's eye effect and weak asterism are known.

Cordierite Gemstones by Colour

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

Cordierite Gemstones by Size

This table shows distribution of Cordierite 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:0.19 cts
Heaviest:10.43 cts
Average:2.47 cts
Total photos:55
Do you have a larger Cordierite? Why not upload a photo?
0.19ct to 1.21ct1.21ct to 2.24ct2.24ct to 3.26ct3.26ct to 4.29ct4.29ct to 5.31ct5.31ct to 6.33ct6.33ct to 7.36ct7.36ct to 8.38ct8.38ct to 9.41ct9.41ct to 10.43ct
General Information
Other Names/Trade Names:
Chemical Formula
Mg
 
2
Al
 
4
Si
 
5
O
 
18
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
More from other references
Photos of natural/un-cut material from mindat.org
Physical Properties of Cordierite
Mohs Hardness7 to 7.5
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Specific Gravity2.56 to 2.66
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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TenacityBrittle
Walter Schumann, Gemstones of the world (2001)
Cleavage QualityGood
Walter Schumann, Gemstones of the world (2001)
FractureUneven,Conchoidal
Walter Schumann, Gemstones of the world (2001)
Optical Properties of Cordierite
Refractive Index1.542 to 1.578
Walter Schumann, Gemstones of the world (2001)
More from other references
Optical CharacterBiaxial/+,-
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Birefringence0.008 to 0.012
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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PleochroismStrong trichroism: colorless to yellowish - pale blue - dark (violet)-blue
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Dispersion0.017
Walter Schumann, Gemstones of the world (2001)
ChatoyancyYes
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Colour
Colour (General)Mostly (violet)-blue
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
More from other references
Causes of ColourViolet to blue, Fe2+-O-Fe3+ charge transfer. Red, hematite and/or lepidocrocite inclusions
W. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011)
TransparencyTransparent,Translucent
Walter Schumann, Gemstones of the world (2001)
More from other references
LustreVitreous,Greasy
Walter Schumann, Gemstones of the world (2001)
Fluorescence & other light emissions
Fluorescence (General)None
Walter Schumann, Gemstones of the world (2001)
Crystallography of Cordierite
Crystal SystemOrthorhombic
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
More from other references
HabitShort prismatic crystals and may be pseudohexagonal
Michael O’Donoghue, Gems, Sixth Edition (2006)
Geological Environment
Where found:Most gem material occurs as water-worn pebbles. Apart from alluvial, occurs in a variety of environments, including altered aluminous and igneous rocks.
Michael O’Donoghue, Gems, Sixth Edition (2006)
Inclusions in Cordierite
Tabular parallel brownish-red iron oxide: may cause glittery effect (bloodshot iolite) - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p 6

Inclusions: hematite, rutile, apatite, mica, etc. - Gemmological Tables, Ulrich Henn and Claudio C. Milisenda, 2004, p 7
Further Information
Mineral information:Cordierite information at mindat.org
Significant Gem Localities
Canada
 
Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 419
Finland
 
  • Southwestern Finland Region
    • Salo
      • Kisko
India
 
  • Karnataka
    • Tumkur District
      • Koratagere Taluk
S. Fernandes (1999)
S. Fernandes (1999)
  • Tamil Nadu
    • Madurai District
S. Fernandes (1999)
S. Fernandes (1999)
Madagascar
 
  • Antananarivo Province
    • Vakinankaratra Region
      • Antsirabe II District
        • Sahanivotry Manandona Commune
Lefevre and Thomas (1997)
Myanmar
 
  • Mandalay Region
    • Pyin-Oo-Lwin District
        • Mogok Valley
Ted Themelis (2008) Gems & mines of Mogok
Norway
 
  • Telemark
    • Kragerø
      • Kragerø Archipelago
      • Sannidal
Russia
 
  • Altai Krai
    • Gornyi Altai
      • Kharlovo
Y. Shelementiev (1999)
Sri Lanka
 
  • Sabaragamuwa Province
    • Ratnapura District
      • Ratnapura
Milisenda and Henn (1999)
USA
 
  • California
    • Lake Co.
      • Mayacmas Mts (Mayacamas Mts)
        • East Mayacmas District
          • Howard Springs
Brice, J.C. (1953), Geology of Lower Lake quadrangle, California: California Division Mines Bulletin 166; Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 314.
  • Connecticut
    • Tolland Co.
      • Union
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