Howlite

Big Photo

USA
9.98 carats
© gemselect.com

Howlite was discovered near Windsor, Nova Scotia in 1868 and named after Henry How, a Canadian chemist, geologist, and mineralogist.

It often forms in nodules which resemble cauliflower heads. The nodules are opaque, white with gray or black veins, often showing web-like pattern. Crystals are very rare and are found in only a couple localities in the world. The maximum size of crystals is about 1 cm.

Howlite is used for cabochons, decorative objects, beads, small carvings or jewelry components. Dyed blue howlite is used as a turquoise substitute and is sometimes marketed as turquenite.

Howlite Gemstones by Colour

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

Howlite Gemstones by Size

This table shows distribution of Howlite 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:2.36 cts
Heaviest:33.94 cts
Average:9.99 cts
Total photos:22
Do you have a larger Howlite? Why not upload a photo?
2.36ct to 5.52ct5.52ct to 8.68ct8.68ct to 11.83ct11.83ct to 14.99ct14.99ct to 18.15ct18.15ct to 21.31ct21.31ct to 24.47ct24.47ct to 27.62ct27.62ct to 30.78ct30.78ct to 33.94ct
General Information
Chemical Formula
Ca
 
2
B
 
5
SiO
 
9
(OH)
 
5
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Photos of natural/un-cut material from mindat.org
Howlite Treatments
Howlite has been dyed various colors and may also be waxed. An elaborate carving was dyed blue to produce a superficial resemblance to turquoise; a test used to identify it was to etch the surface with acid and observe melting of the howlite with a hot needle (Crowningshield, 1969) – Nassau (1984)
Dyed blue to imitate turquoise (and lapis lazuli). Acetone test may reveal the dye - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p 5
Physical Properties of Howlite
Mohs Hardness3 to 3.5
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Specific Gravity2.45 to 2.58
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Cleavage QualityNone
Arthur Thomas, Gemstones (2009)
FractureUneven
Arthur Thomas, Gemstones (2009)
Optical Properties of Howlite
Refractive Index1.583 to 1.608
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Optical CharacterBiaxial/-
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Birefringence0.019
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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PleochroismNil
Arthur Thomas, Gemstones (2009)
DispersionNil
Arthur Thomas, Gemstones (2009)
Colour
Colour (General)Natural color: white, commonly with gray to black "spiderweb" matrix.
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Colour (Chelsea Filter)Dyed howlite: pink to red
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Causes of ColourBlue, dyes exclusively
W. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011)
TransparencyOpaque
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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LustreVitreous,Dull (Earthy)
Arthur Thomas, Gemstones (2009) sub-vitreous
Fluorescence & other light emissions
Fluorescence (Short Wave UV)Occasionally orange
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Fluorescence (Long-Wave UV)Brownish-yellow
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Crystallography of Howlite
Crystal SystemMonoclinic
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:Howlite is found in borate deposits.
Michael O’Donoghue, Gems, Sixth Edition (2006)
Further Information
Mineral information:Howlite information at mindat.org
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