Milk Opal (Porcelain Opal)

Pinfire play-of-colour against a semi-opaque milky white body colour.
General Information
A variety or type of:Common Opal, which is a variety of Opal
Other Names/Trade Names:
Chemical Formula
SiO
 
2
· nH
 
2
O
Walter Schumann, Gemstones of the world (2001)
Physical Properties of Milk Opal
Mohs Hardness5.5 to 6.5
Walter Schumann, Gemstones of the world (2001)
Specific Gravity1.98 to 2.50
Walter Schumann, Gemstones of the world (2001)
TenacityBrittle
Walter Schumann, Gemstones of the world (2001)
Cleavage QualityNone
Walter Schumann, Gemstones of the world (2001)
FractureConchoidal,Splintery
Walter Schumann, Gemstones of the world (2001)
Optical Properties of Milk Opal
Refractive Index1.37 to 1.52
Walter Schumann, Gemstones of the world (2001)
BirefringenceNone
Walter Schumann, Gemstones of the world (2001)
PleochroismAbsent
Walter Schumann, Gemstones of the world (2001)
Colour
Colour (General)White, milky body colour, play-of-colour
Walter Schumann, Gemstones of the world (2001)
TransparencyTranslucent,Opaque
Walter Schumann, Gemstones of the world (2001)
Crystallography of Milk Opal
Crystal SystemAmorphous
Walter Schumann, Gemstones of the world (2001)
HabitKidney- or grape-shaped aggregates.
Walter Schumann, Gemstones of the world (2001)
Further Information
Mineral information:Milk Opal information at mindat.org
Significant Gem Localities
Australia
 
  • South Australia
    • Central North
    • North West Province
      • Mintabie district
USA
 
  • Nevada
    • Humboldt Co.
      • Virgin Valley
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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