| General Information |
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| A variety or type of: | Precious Opal, which is a variety of Opal |
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| Chemical Formula | Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) |
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| Physical Properties of Crystal Opal |
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| Mohs Hardness | 5.5 to 6.5Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) |
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| Specific Gravity | 1.97 to 2.22Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) |
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| Tenacity | BrittleWalter Schumann, Gemstones of the world (2001) |
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| Cleavage Quality | NoneWalter Schumann, Gemstones of the world (2001) |
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| Fracture | ConchoidalArthur Thomas, Gemstones (2009) |
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| Optical Properties of Crystal Opal |
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| Refractive Index | 1.370 to 1..470Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) |
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| Optical Character | IsotropicArthur Thomas, Gemstones (2009) |
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| Birefringence | NoneWalter Schumann, Gemstones of the world (2001) |
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| Pleochroism | AbsentWalter Schumann, Gemstones of the world (2001) |
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| Dispersion | NoneWalter Schumann, Gemstones of the world (2001) |
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| Colour |
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| Colour (General) | Black, white, colourless, yellow, bluishGemdat.org, Management Team (2012) |
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| Transparency | Transparent,TranslucentGemdat.org, Management Team (2012) |
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| Lustre | VitreousArthur Thomas, Gemstones (2009) |
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| Crystallography of Crystal Opal |
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| Crystal System | AmorphousHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) |
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| Habit | MassiveArthur Thomas, Gemstones (2009) |
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| Further Information |
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| Mineral information: | Crystal Opal information at mindat.org |
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| Significant Gem Localities |
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| Australia | | |
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| | | USA | | |
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| Holzhey (1997) |
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