Precious Opal

Opal is often impregnated with plastic to improve appearance. - Gemstones of the world, Walter Schumann, 2001, p 150 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 5 to 6.5Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) 1.98 to 2.25Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) BrittleWalter Schumann, Gemstones of the world (2001) NoneWalter Schumann, Gemstones of the world (2001) Conchoidal,SplinteryWalter Schumann, Gemstones of the world (2001) More from other references 1.370 to 1.470Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) IsotropicArthur Thomas, Gemstones (2009) NoneWalter Schumann, Gemstones of the world (2001) AbsentWalter Schumann, Gemstones of the world (2001) NoneWalter Schumann, Gemstones of the world (2001) All colors, play of colorWalter Schumann, Gemstones of the world (2001) More from other references Multicolors (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 inclusionsW. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011) Transparent,Translucent,OpaqueUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) VitreousArthur Thomas, Gemstones (2009) AmorphousHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) Kidney- or grape-shaped aggregatesWalter Schumann, Gemstones of the world (2001) More from other references Swirl-like exsolutions, goethite, chalcedony etc., liquid- and multiphase inclusions - Gemmological Tables, Ulrich Henn and Claudio C. Milisenda, 2004, p 1 Precious Opal information at mindat.org Australia  [var: Black Opal] Opal, Lithographie, 2007 No reference listed Cooper and Neville (2007) [var: Boulder Opal] Opal, Lithographie, 2007 [var: Boulder Opal] [var: Boulder Opal] Dennis Tryon collection John Nijhuis. [var: Black Opal] Opal, Lithographie, 2007 No reference listed Brazil  Canada  www.em.gov.bc.ca/cf/minfile Ethiopia  [var: White Opal] Indonesia  Laurs (2001) Mexico  mindat.org mindat.org Peru  [var: White Opal] USA  Extra Lapis - English No. 10 Opal Gaber (2007) USGS Bull 1538D Holzhey (1997)