Boulder Opal

Big Photo

Australia
16.32 carats
© gemselect.com

This variety of Precious Opal was first found in Queensland, Australia in 1869.

It is a Precious Opal that is embedded in the ironstone matrix and routinely cut with it as part of the gem.

Each piece is unique, that is why it can't be used for mass produced jewelry.

Boulder Opal Gemstones by Colour

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

Boulder Opal Gemstones by Size

This table shows distribution of Boulder 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:2.17 cts
Heaviest:206.2 cts
Average:25.47 cts
Total photos:45
Do you have a larger Boulder Opal? Why not upload a photo?
2.17ct to 22.57ct22.57ct to 42.98ct42.98ct to 63.38ct63.38ct to 83.78ct83.78ct to 104.19ct104.19ct to 124.59ct124.59ct to 144.99ct144.99ct to 165.39ct165.39ct to 185.80ct185.80ct to 206.20ct
General Information
A variety or type of:Precious Opal, which is a variety of Opal
Chemical Formula
SiO
 
2
+ H
 
2
O
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Photos of natural/un-cut material from mindat.org
Physical Properties of Boulder 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
Arthur Thomas, Gemstones (2009)
Optical Properties of Boulder 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)Dark base surface, play-of-color
Walter Schumann, Gemstones of the world (2001)
TransparencyTransparent,Translucent,Opaque
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
LustreVitreous
Arthur Thomas, Gemstones (2009)
Crystallography of Boulder Opal
Crystal SystemAmorphous
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
HabitMassive
Arthur Thomas, Gemstones (2009)
Geological Environment
Where found:Occurs as patches, seams, blobs, or thin veins in ironstone concretions.
Lithographie, Opal (2007)
Further Information
Mineral information:Boulder Opal information at mindat.org
Significant Gem Localities
Australia
 
  • New South Wales
    • Finch Co.
  • Queensland
    • Paroo Shire
    • Quilpie Shire
Opal, Lithographie, 2007
    • Winton Shire
Dennis Tryon collection
Brazil
 
  • Pará
    • São Geraldo do Araguaia
Canada
 
  • British Columbia
    • Vernon Mining Division
      • Vernon
Can.Rockhound v.3, no.1
Copyright © Jolyon & Katya Ralph 1993-2017. Site Map. Locality, gem & photograph data are the copyright of the individuals who submitted them. For more information please contact the . Gemdat.org is an online information resource dedicated to providing free gemmological information to all.