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Key terms: opal color black silica structure fire spheres layer crystal australia thin stacked planes precious opal wood nevada packed gemstone consisting glass produce display doublet varieties play of color black opal matrix deposits valley synthetics quartz termed commonly quality visible wavelength internal diffraction siliceous correctly amorphous water content regularity fire opals queensland boulder opal crystal opal microcrystalline south australia crystal structure Search external links cited by footnotes on Wikipedia page Opal: |
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