Benitoite

Big Photo

San Benito Co., California, USA
1.67 carats
© Rarestone.com

Benitoite was discovered at the beginning of the 20th century in San Benito County (therefore the name), California, USA.

A very rare gem with beautiful colour, high birefringence and dispersion, tough, does not have heat sensitivity, exhibits strong blue fluorescence under SW UV. Gem-quality crystals are usually small (rarely larger than 1 carat). The largest facetted benitoite on public display is a 7.5 ct gem in the Smithsonian museum. There are other larger flawless stones in existence, all in private collections.

Benitoite Gemstones by Colour

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

Benitoite Gemstones by Size

This table shows distribution of Benitoite 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:0.03 cts
Heaviest:2.63 cts
Average:0.72 cts
Total photos:28
Do you have a larger Benitoite? Why not upload a photo?
0.03ct to 0.29ct0.29ct to 0.55ct0.55ct to 0.81ct0.81ct to 1.07ct1.07ct to 1.33ct1.33ct to 1.59ct1.59ct to 1.85ct1.85ct to 2.11ct2.11ct to 2.37ct2.37ct to 2.63ct
General Information
Chemical Formula
BaTiSi
 
3
O
 
9
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Significant stones
ImageNameWeightCountry of OriginCurrent Owner
Eacret BenitoiteUSASmithsonian Institution
Photos of natural/un-cut material from mindat.org
Benitoite Treatments
The deep blue color observed in some benitoite may have the same iron-titanium charge-transfer origin as does the blue in sapphire. It is doubtful that any of the corundum heat treatments could be applied successfully, however, since benitoite has a much lower melting point, being a silicate of composition BaTiSi3O9. G. Rossman has found (unpublished data) that benitoite gradually loses its blue color on heating in air at 600°C for 19 h. Irradiation with cobalt 60 returned some of the color center that is unrelated to the natural color – Nassau (1984)
Heat-treatment may produce pinkish orange colors - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p. 3
Only the rare colourless benitoite can be heat-treated and will change to peachy/orange colour. Blue benitoite cannot be heat-treated. - Personal communication, 2014.
Physical Properties of Benitoite
Mohs Hardness6 to 6.5
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Specific Gravity3.61 to 3.68
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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TenacityBrittle
Walter Schumann, Gemstones of the world (2001)
Cleavage QualityIndistinct
Walter Schumann, Gemstones of the world (2001)
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FractureConchoidal
Arthur Thomas, Gemstones (2009)
Optical Properties of Benitoite
Refractive Index1.757 to 1.804
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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Birefringence0.047
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) DoublingMore from other references
PleochroismStrong dichroism: blue - colorless
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Dispersion0.039 to 0.046
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Colour
Colour (General)Blue, purple, pink, colourless
Walter Schumann, Gemstones of the world (2001)
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Causes of ColourBlue, Fe2+-O-Ti4+ charge transfer
W. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011)
TransparencyTransparent,Translucent
Arthur Thomas, Gemstones (2009)
LustreAdamantine,Subadamantine,Vitreous
Walter Schumann, Gemstones of the world (2001)
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Fluorescence & other light emissions
Fluorescence (Short Wave UV)Weak to bright chalky blue.
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Fluorescence (Long-Wave UV)Inert
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Crystallography of Benitoite
Crystal SystemHexagonal
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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HabitTabular
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Geological Environment
Where found:In natrolite veins cutting glaucophane schist in a serpentine body (San Benito Co., California, USA); in a magnesio-riebeckite-quartz phlogopite-albite dike cutting serpentinite (Ohmi, Japan).
Anthony et al, Handbook of Mineralogy (2001)
Inclusions in Benitoite
Color zoning. Crystals inclusions such as tiny white crossite fibers - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p. 3
Inclusions of crossite fibers, micro-neptunite and a newly classified micromineral Barioparovskite. - Personal communication, 2014.
Further Information
Mineral information:Benitoite information at mindat.org
Significant Gem Localities
USA
 
  • California
    • San Benito Co.
      • Diablo Range
        • New Idria District
          • Santa Rita Peak
NJMMh, 16 (1987) / Wise, W.S & Gill, R.H. (1977): Minerals of the Benitoite Gem mine. Mineralogical Record 8, 442-452
Copyright © Jolyon & Katya Ralph 1993-2019. Site Map. Locality, gem & photograph data are the copyright of the individuals who submitted them. For more information please contact the . Gemdat.org is an online information resource dedicated to providing free gemmological information to all.