Spinel

Rubies and spinels may show similar colors. One of the simplest ways to distinguish these gems is to test for double refraction with a dichroscope. Since spinels have an isometric crystal structure, they have no double refraction. On the other hand, rubies do have double refraction. Brilliant-cut oval spinel, 6.88 cts, recut by AGTA Spectrum Award-winner Mark Kaufman. Mogok gem tract, Myanmar. © Rob Lavinsky, www.iRocks.com. Used with permission.

Article: Table of Refractive Indices and Double Refraction of Selected Gems

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