| General Information |
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| Chemical Formula | Michael O’Donoghue, Gems, Sixth Edition (2006) More from other references |
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| Howlite Treatments |
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Massive howlite, Ca2B5Si9(OH)5 is a soft, white, sometimes black-banded material occasionally used for beads and carving. It 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 |
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| Mohs Hardness | 3 to 3.5Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Specific Gravity | 2.45 to 2.58Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Cleavage Quality | NoneArthur Thomas, Gemstones (2009) |
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| Fracture | UnevenArthur Thomas, Gemstones (2009) |
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| Optical Properties of Howlite |
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| Refractive Index | 1.583 to 1.608Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Optical Character | Biaxial/-Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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| Birefringence | 0.019Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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| Pleochroism | NilArthur Thomas, Gemstones (2009) |
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| Dispersion | NilArthur Thomas, Gemstones (2009) |
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| Colour |
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| Colour (General) | Natural color: white, commonly with gray to black "spiderweb" matrix.Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Colour (Chelsea Filter) | Dyed howlite: pink to redHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) |
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| Causes of Colour | Blue, dyes exclusivelyW. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011) |
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| Transparency | OpaqueUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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| Lustre | Vitreous,Dull (Earthy)Arthur Thomas, Gemstones (2009) |
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| Fluorescence & other light emissions |
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| Fluorescence (Short Wave UV) | Occasionally orangeUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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| Fluorescence (Long-Wave UV) | Brownish-yellowUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
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| Crystallography of Howlite |
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| Crystal System | MonoclinicHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references |
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| Habit | TabularMichael O’Donoghue, Gems, Sixth Edition (2006) More from other references |
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| Geological Environment |
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| Where found: | Howlite is found in borate deposits.Michael O’Donoghue, Gems, Sixth Edition (2006) |
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| Further Information |
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| Mineral information: | Howlite information at mindat.org |
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