Amazing color in this 10.85 Ct Contra Luz Opal. This Contra Luz is from our B.C. Opal Mine.
Contra-luz: "against the light" shows phenomenal color with transmitted light
The contraluz opalAmerican Contra Luz Opal -2 is found worldwide, only a tiny percentage is precious. Each location is idiosyncratic, with different base colors characteristic of different regions.
Australia is the primary source and known for its whites, blacks, boulder, and jelly.
Mexico and Oregon material are similar, mostly jelly in water clear to white and yellow through Nehi orange found in Rhyolite matrix, primary sources for contra-luz.
Brazil produces slightly harder precious white opal and much common fire opal for faceting, usually hazy yellow to light orange, often large.
Peru — common blue opal — some greenish, usually seen as beads.
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Precious opal shows a variable interplay of internal colors, and though it is a mineraloid, it has an internal structure. At microscopic scales, precious opal is composed of silica spheres some 150 to 300 nm in diameter in a hexagonal or cubic close-packed lattice. It was shown by J. V. Sanders in the mid-1960s, that these ordered silica spheres produce the internal colors by causing the interference and diffraction of light passing through the microstructure of the opal. The regularity of the sizes and the packing of these spheres determines the quality of precious opal. Where the distance between the regularly packed planes of spheres is around half the wavelength of a component of visible light, the light of that wavelength may be subject to diffraction from the grating created by the stacked planes. The colors that are observed are determined by the spacing between the planes and the orientation of planes with respect to the incident light. The process can be described by Bragg's law of diffraction.
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