The Color of Topaz

Abstract

Topaz, if it is of the ideal composition-free of minor impurities and free from exposure to natural (or laboratory) irradiation-would be colorless because the primary chemical components of topaz (Al^(3+), Si^(4+), O^(2-), OH^-, and F^-) do not absorb light in the visible portion of the spectrum. Numerous examples of natural colorless topaz have been found and many brown topazes become colorless when exposed to prolonged sunlight. Topaz also occurs in a variety of colors ranging through yellow, orange, brown, pink, violet, and blue. In contrast to that of many other mineral species, most of the colors of topaz, with the exception of pink, are the result of either natural or laboratory irradiation. Comparatively few studies had addressed the origin of color in topaz until laboratory-irradiated blue topaz was introduced into the market. Determining the atomic details of color caused by irradiation is difficult, and therefore, conflicting interpretations have developed and remain to this day.

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