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Most Russian hydrothermal synthetic rubies and pink, orange, green, blue, and violet sapphires--colored by chromium and/or nickel--reveal diagnostic zigzag or mosaic-like growth structures associated with color zoning. When the samples are properly oriented, these internal patterns are easily recognized using a standard gemological microscope in conjunction with immersion or fiber-optic illumination. Pleochroism is also useful to separate chromium-free blue-to-green synthetic sapphires from their natural counterparts. Samples colored by a combination of chromium, nickel, and iron are also described. |
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