| General Information |
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| A variety or type of: | Common Opal, which is a variety of Opal |
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| Other Names/Trade Names: | |
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| Chemical Formula | Walter Schumann, Gemstones of the world (2001) |
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| Physical Properties of Milk Opal |
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| Mohs Hardness | 5.5 to 6.5Walter Schumann, Gemstones of the world (2001) |
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| Specific Gravity | 1.98 to 2.50Walter Schumann, Gemstones of the world (2001) |
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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 | Conchoidal,SplinteryWalter Schumann, Gemstones of the world (2001) |
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| Optical Properties of Milk Opal |
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| Refractive Index | 1.37 to 1.52Walter Schumann, Gemstones of the world (2001) |
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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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| Colour |
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| Colour (General) | White, milky body colour, play-of-colourWalter Schumann, Gemstones of the world (2001) |
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| Transparency | Translucent,OpaqueWalter Schumann, Gemstones of the world (2001) |
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| Crystallography of Milk Opal |
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| Crystal System | AmorphousWalter Schumann, Gemstones of the world (2001) |
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| Habit | Kidney- or grape-shaped aggregates.Walter Schumann, Gemstones of the world (2001) |
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| Further Information |
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| Mineral information: | Milk Opal information at mindat.org |
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| Significant Gem Localities |
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| Australia | |
- Aṉangu Pitjantjatjara Yankunytjatjara (APY; APY Lands)
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- Pastoral Unincorporated Area
| | | USA | | |
| NBMG files No. 50600003; Nevada Bureau of Mines and Geology NBMG Open-File Report 96-3 By Stephen B. Castor, Christopher D. Henry, Lisa A. Shevenell |
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