Common Opal

Big Photo

Girasol
Ethiopia
6.28 carats
© Kosnar Gem Co.

Common opal is opaque, rarely translucent, and shows no play-of-colour. A wide variety of trade names are used.

Common Opal Gemstones by Colour

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

Common Opal Gemstones by Size

This table shows distribution of Common Opal 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:1.10 cts
Heaviest:28.87 cts
Average:4.53 cts
Total photos:15
Do you have a larger Common Opal? Why not upload a photo?
1.10ct to 3.88ct3.88ct to 6.65ct6.65ct to 9.43ct9.43ct to 12.21ct12.21ct to 14.99ct14.99ct to 17.76ct17.76ct to 20.54ct20.54ct to 23.32ct23.32ct to 26.09ct26.09ct to 28.87ct
General Information
A variety or type of:Opal
Varieties/Types:
Agate Opal - Opal showing concentric banding as in agate.
Andean Opal - A greenish-blue variety of opal found in Peru.
Girasol - Bluish-white translucent Opal with reddish reflections.
Honey Opal - An orange-brown Common opal.
Hyalite - Colourless, water-clear opal with a strong sheen.
Hydrophane - A milky variety of Opal that turns translucent or transparent when immersed in water.
Jasper Opal - A brecciated Jasper cemented by opal.
Milk Opal - A white Common opal.
Moss Opal - Milky opal containing dendritic inclusions
Prase Opal - A green variety of Common opal.
Semiopal - Historic name for an opal without opalescence
Wax Opal - A yellow-to brown Opal with a waxy lustre.
Wood Opal - Petrified wood replaced with Opal.
Chemical Formula
SiO
 
2
· nH
 
2
O
Walter Schumann, Gemstones of the world (2001)
Photos of natural/un-cut material from mindat.org
Physical Properties of Common 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 Common 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)
DispersionNone
Walter Schumann, Gemstones of the world (2001)
Colour
Colour (General)All colours
Walter Schumann, Gemstones of the world (2001)
TransparencyTranslucent,Opaque
Walter Schumann, Gemstones of the world (2001)
Crystallography of Common 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:Common Opal information at mindat.org
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