Precious Opal

Big Photo

Black Opal
Ethiopia
8.55 carats
© gemselect.com

The special characteristic of these gems is their play-of-colour, a display of rainbow-like hues, which (especially in rounded cut forms) changes with the angle of observation.

Opal always contains water (3 - 30%). It can happen that in the course of time, the stone loses water, cracks, and the play-of-colour diminishes. Special care should be taken for storing it.
100 photos

Precious Opal Gemstones by Colour

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

Precious Opal Gemstones by Size

This table shows distribution of Precious 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:0.28 cts
Heaviest:206.2 cts
Average:15.86 cts
Total photos:102
Do you have a larger Precious Opal? Why not upload a photo?
0.28ct to 20.87ct20.87ct to 41.46ct41.46ct to 62.06ct62.06ct to 82.65ct82.65ct to 103.24ct103.24ct to 123.83ct123.83ct to 144.42ct144.42ct to 165.02ct165.02ct to 185.61ct185.61ct to 206.20ct
General Information
A variety or type of:Opal
Varieties/Types:
Black Opal - The variety of Precious Opal with a dark background colour.
Boulder Opal - A variety of Precious Opal found in Queensland, Australia.
Crystal Opal - Transparent to translucent Precious Opal where colour play is visible both on the surface and in the interior.
Harlequin Opal - Transparent to translucent Precious Opal with effective mosaic-like colour patterns.
Matrix Opal - A rock consisting of a (usually) silicified matrix containing veins or blebs of Precious opal.
Water Opal - A transparent Precious opal with a gelatinous appearance and a bluish sheen.
White Opal - Precious Opal with a white background.
Chemical Formula
SiO
 
2
 · nH
 
2
O
Gemdat.org, Management Team (2012)
Photos of natural/un-cut material from mindat.org
Precious Opal Treatments
Opal is often impregnated with plastic to improve appearance. - Gemstones of the world, Walter Schumann, 2001, p 150
Synthetic Precious Opal
Synthetic opal: RI 1.440 - 1.450; opt. isotropic; SG 1.74 - 2.07; Colours: colourless, white, black, red; Play of colour: red, orange, yellow, green, blue, violet; Transparent to opaque; Hardness 5.5 - 6.5. Clearly separated colour patches, "lizard-skin effect", columnar structure perpendicular to the "lizard-skin effect" - Gemmological Tables, Ulrich Henn and Claudio C. Milisenda, 2004, p 1
Physical Properties of Precious Opal
Mohs Hardness5 to 6.5
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Specific Gravity1.98 to 2.25
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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)
More from other references
Optical Properties of Precious Opal
Refractive Index1.370 to 1.470
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Optical CharacterIsotropic
Arthur Thomas, Gemstones (2009)
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 colors, play of color
Walter Schumann, Gemstones of the world (2001)
More from other references
Causes of ColourMulticolors (play of color opal), diffraction by the regular stacking of silica spheres. Orange to red (fire opal), microscopic to sub-microscopic inclusions of iron hydrous oxides. Green (prase opal), microscopic to submicroscopic nickeliferous clay-like inclusions
W. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011)
TransparencyTransparent,Translucent,Opaque
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
LustreVitreous
Arthur Thomas, Gemstones (2009)
Crystallography of Precious Opal
Crystal SystemAmorphous
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
HabitKidney- or grape-shaped aggregates
Walter Schumann, Gemstones of the world (2001)
More from other references
Inclusions in Precious Opal
Swirl-like exsolutions, goethite, chalcedony etc., liquid- and multiphase inclusions - Gemmological Tables, Ulrich Henn and Claudio C. Milisenda, 2004, p 1
Further Information
Mineral information:Precious Opal information at mindat.org
Significant Gem Localities
Australia
 
  • New South Wales
    • Finch Co.
[var: Black Opal] Opal, Lithographie, 2007
    • Narran Co.
      • Angledool
    • Yungnulgra Co.
No reference listed
  • Queensland
    • Paroo Shire
    • Quilpie Shire
Cooper and Neville (2007)
[var: Boulder Opal] Opal, Lithographie, 2007
    • Winton Shire
[var: Boulder Opal]
[var: Boulder Opal] Dennis Tryon collection
  • South Australia
    • Andamooka Ranges
[var: Black Opal] Opal, Lithographie, 2007
    • Central North
No reference listed
    • North West Province
      • Mintabie
John Nijhuis.
Brazil
 
  • Pará
    • São Geraldo do Araguaia
Canada
 
  • British Columbia
    • Vernon Mining Division
      • Vernon
www.em.gov.bc.ca/cf/minfile
Ethiopia
 
  • Amhara Region
    • North Shewa Zone
[var: White Opal]
    • North Wollo Zone
      • Delanta Woreda
Indonesia
 
  • Banten Province
    • Lebak Regency
Laurs (2001)
Mexico
 
  • Jalisco
    • Magdalena Municipality
      • Magdalena
mindat.org
mindat.org
Peru
 
  • Ica
    • Ica Province
      • Ica District
[var: White Opal]
USA
 
  • Idaho
    • Clark County
      • Spencer
Extra Lapis - English No. 10 Opal
  • Louisiana
    • Vernon Parish
Gaber (2007)
  • Nevada
    • Humboldt County
USGS Bull 1538D
  • Oregon
    • Morrow County
Holzhey (1997)
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